Can you just please explain what problem it solves and why you think the market wants the utility of a larger screen for ~2x the price?
You mean Apple didn't come to you for your opinion, but instead probably utilised millions of dollars of research based on the world market?
Products don't suit everybody, it's clear you feel you don't need a foldable, great, but the world is not you.
Some people may want one.
I bought a Pixel 10 Pro Fold a few weeks ago, got it for a bargain price, almost half price at £875 (brand new), I switched from a regular Pixel 9 Pro, when the device is folded it is no more than a couple of millimetres thicker, not even noticeable, yet when it's open it's very thin, easy to hold and I've found it excellent when I'm working away to watch movies / TV shows on.
So yes, it won't be for everyone, but that doesn't mean there isn't a market for them. I'm fairly sure when Apple first announced AirPods they were ridiculed a lot, look at us now, everyone wears them.