Because noone in the world can be firmly commited to start from the beginning NOW and be on concert pianist level in 10 years. I'm not saying you cannot have such an intention, nor that it is impossible. But you can never make such a promise. No matter what the OP thinks today, he/she might have a total different opinion in one year from now, because it is like that with all new projects we start. We cannot know for sure. And it is perfectly OK to change your mind, it is not a "moral" issue or something like that.
Yes, I agree with you that a digital has to be real good, and the best ones are certainly not cheap. Personally I don't like the Casios at all, I have tried them. But you really have to TRY. What you need is an instrument that you truly enjoy to work with. After all, there are piano players out there who really love their Casios ...
So, I have a digital baby grand and it works for me - in the aspect that I really, really like to play it. I can practice for hours. I like the sound, the touch, the very look of it. Of course there will always be some Knowhow wrinkling his nose at such and instrument and say some dry words about it not being the real thing. (Yeah, I have met them.) So, perhaps not, but people who hear me play (on acoustic pianos) don't seem to question that I know how to play the piano. Even if I am just an amateur. So when I say that you can learn to play on a digital and enjoy the process too, it is not my GUESS or my BELIEF, it is something I KNOW from own experience.
Where I live, in Sweden, you can get an upright (although not the best kinds of uprights, maybe) practically for free. Thats is, if you arrange with the move. And pay a piano tuner to get it in decent shape. And if you have a tolerant family, neighbours etcetera. That is why owners of these pianos often are quite desperate in their attempts to get rid of them ... And that is why an absolute beginner should be a bit patient. Digitals are easier to move in, and to move out, and to sell. And they don't need maintenance, tuning and so on.
So, highest priority is to get a good teacher and a decent piano for daily practice. I say decent, not "anything with black and white keys". Then you can start thinking of the next step: either you upgrade to an even better instrument OR you arrange that you get access to such an instrument OR you decide that this was not a good idea after all and focus on other interests. But again, getting rid of an acoustic can be a rather complicated issue, and don't you think you need some experience in order to find an acoustic that you really like?