The answer to questions like that is always money. Apple have a monopoly on selling apps on that run on Apple hardware. There is no measurable short-term benefit to them from making the user experience better. In fact they probably figure it'd hurt revenue.
As it stands the app store has about 20 slots that make serious money. Every app company wants in those slots and will do anything for it, eg give up 30% of their revenue and indulge various forms of payola.
Apple have created an artificial scarcity and it makes them something like 10 billion a year. And thanks to the monopoly enforced by crypto, there is no possibility of a competitor forcing them to change.
It's the perfect cash cow. Why screw up a good thing?
Large companies don't always do a good job of simple things, for all sorts of banal reasons related to specific people in management, organisational politics, etc.
It's terrible and i can only imagine how much this hurts devs. Apple really doesn't care about the long tail.