When you start out playing the piano, there is quite a bit of social incentive to do so.
I started quite young (3 years old) so to me piano was just something that has always been a part of my life. When I was a teen I did enjoy winning competitions and performing on stage and being the centre of attention, but later on after I starting doing it for a career that feeling pretty much vanished. It was the musical connection with individuals that to me was more personally rewarding than having large groups of people be entertained by my playing and presentations.
Once you reach a stage where you can walk up to a piano and play something decent, that gives you a fun skill to show off. However, once you get past a certain point, it all seems to be very similar to the layman (or not? music is complicated.)
Practically everyone enjoy hearing something they know more so than some obscure virtuosic piano piece. I remember the 2nd solo concert I ever did it was full of lesser known virtuosic pieces and it was no where near as popular as my 1st concert which had a lot of classical favorites that many people knew. When I was younger I was learning more difficult pieces to see how far I could go, eventually that endevour became boring and I much preferred to study music that I enjoyed myself and that others enjoy. It is important to learn popular music that is trending so you can connect with the public more readily. I used to be like a musical hermit learning only obscure difficult music to push myself but nowadays, although I still like playing obscure difficult stuff, I have balanced it with a lot more socialable repertoire.
You spend hundreds of hours, often making subtle improvements which often aren't apparent to someone in the audience.
This is a real reason why I think sight reading is so powerful. No longer did I have to labor hours and hours learning something that people really didn't know or care that I had poured so much into. Sight reading freed me from this issue, theres never hundred hours to learn a piece. I could pour thousands and thousands of hours into sight reading training and people would notice it because my sight reading skills improve and I can readily play more and more pieces immediately without any practice at all.
There's virtually no difference in a lot of situations between playing decently and playing amazingly well, because listeners need to be paying attention and/or have a musical ear to tell the difference.
For me at least it's not about what others hear that is important but from what you hear yourself. There is a lot of pleasure playing something as "perfect" as possible and the majority of that pleasure is for ourselves.
The more musically interesting pieces you try to spend time on will be less interesting to most people than a cliched Chopin waltz.
I would argue that Chopin waltz will put many people to sleep and bore them. But what we feel as musicians is most important. I can play certain pieces and feel deep emotions and recall memories from the past, it's precious to me first and foremost. I really don't care what others think about it, I feel a power that is highly desirable and beneficial to me.
Music becomes increasingly subjective. At the starting, the basics of phrasing etc are almost "universal", in the sense that there is to a large extent a concept of what sounds better or worse, which will be apparent to many people and generally accepted. Not in the sense of an authority governing it, but people will just "know" intuitively when something is musical or not, and the reason for that boils down to such concepts which are tacitly acquired.
Music can be very subjective because we are all individals in the experience of it. I think those who think too much with the listening experience of music miss out on a lot. First and foremost you just need to use your ears, nothing else is required. Tribal people who live in the forest who never heard classical music before can even appreciate it when they hear it for the first time, some of course don't like it but others are captivated by it. Do they care if someone performed something faster, or slower or louder or softer?? They really don't care, it is insigificant. Do you listen to tribal music and think that their drums should change in a way to be better?
If you play completely for your own satisfaction, it feels like you miss out on the communication aspect of it. If you play to communicate it to other people, however, the a majority of people will not get the music beyond a rather superficial level, so you feel defeated.
It's one reason why I am teacher, I enjoy seeing the unique musical journey everyone goes through and be a part of it. It's more than just the piano and music though, behaviour and thoughts with the piano represent a lot about someones life. If you discuss music with the right people it is exciting but with many others it is just a generalize topic which they don't want to go so deep into. Probably 90% of my friends and family are like that, they don't care that I play the piano which is totally fine with me, piano playing does not define who I am.
Then, do you play for other pianists, or critics, or people who you in general believe truly understand music?
Other pianists can give good ideas especially if they have played pieces you present to them but I would be wary who you deal with because some musicians can be like nuclear radiation (you don't realize you've been poisoned until its too late) and others belong in an asylum (crazy ideas that they must make everyone believe). Critics are just boring why bother, unless you like word salad.
Or on the other hand, do you believe that a truly good piano performance is like a shining beacon of light, self-evident to anyone who sees it?
Of course not, there is no universal truth when it comes to appreciating music. I could imagine perhaps if we heard music from a Godly source it might be of a type of sound we have never heard but which touches such a deep musical emotion that we all cannot help but be affected. That doesn't occur in our material world however but we can catch glimpses of it but its always a personal experience it never will cause everyone to react the same way.
What motivates you to keep improving once you are at that point? Why do you keep playing?
We need some sort of skill we can see improvement upon or feel confident that pouring work into will produce us beneficial returns for the investment. I strongly believe sight reading skills are the endgame. If repertoire study was the endgame I think I might have given up personally playing the piano. The process of learning a piece by memory and then only moving onto something else is not that interesting to me. I enjoyed it early on in my studies but eventually I didn't enjoy just throwing countless hours into a work before I could enjoy it. Faster satisfaction is the go, but it requires a huge amount of reading training to actually to get to that point.
I'm excited with sight reading more so than any other piano skill, the last year or so I have been pushing my photographic memory, being able to quikcly glance at any bar of music and still see all the notes in my mind. I've been studying piano 37 years and I'm still learning new ideas, that is exciting. I was encouraged to do this after years of dreaming about music, I could see music in my mind and my hands playing that music in my dreams, that state can exist when awake and sight reading which was a great discovery for me. To have the sheet music physically infront of you, mentally in the mind and automated in the hands/ears, the three visions of reading.