Since the title says "beginning", I've assumed that we are talking about beginners. I'm looking at this from a personal dual perspective. I started a new instrument as an adult, and we went through the beginner material awful fast. I have restarted that instrument, from scratch, even though my last grade was grade 7. Meanwhile I went back to piano after decades, having self-taught as a child, and here, too, I need to get the proper technique going, and rework many things. In these ways I am in a sense artificially in "beginner mode". (I'm also a trained teacher for the formative years.)
So what I find in "beginner mode" is that you need to concentrate on lots of new things which an advanced player takes for granted and does automatically. If you have too much to do, you'll start flubbing it, or be scattered among "too much". The focus is on the essential things, and a piece is the practice ground for it. The student might be concentrating on reading/matching notes one time, moving evenly and with ease another time, doing dynamics effectively another time etc. This is better done with shorter pieces, because more time is spent on a line and more effort must be put into it. Someone who is already a musician won't be aware of this. A teacher might lose sight of it.
I would ask who this is for? The "public presentations" is a start. So it's for the audience, to entertain them? Why? Aren't recitals for the student, to teach the student things? If it's for the audience, there is a mix-up of priorities. If parents are not impressed, and want to be impressed by "nice sounding impressive music", then the teacher has to educate and guide the parents. If the teacher is tired of teaching boring beginner pieces, either he should stuff it up, or not teach beginners maybe. The decisions have to be for the sake of the learner. That is not what I am seeing in the opening post, when public presentations being interesting --- especially when the student is motivated, but that doesn't seem to be enough.