I bought a cheaply iPhone case for my XR. Fell apart after a few months. Bought another. The edge around the screen and camera was not raised enough. I got the one I have now on sale, but it retails for like $30 plus. It’s also the best one so far.

Cases are like cables. You need to have them available, and the only way to guarantee that they're available is to make them yourself (given that they're not based on industry standards). If case you bought 2 years ago still fit on the new phone today, then there's not much pressure for Apple to have a case, but since cases are tied to specific phone designs and form-factors, the only way to guarantee high-quality cases available at launch is to make them.

It occurs to me, cases are also like chargers. Nobody questions why apple sells their own USB-C charger even though you could in theory use a generic USB-C charger.

They've been going 2 generations with each form factor. 7/8 were identical, X and XS are identical. I do appreciate that, even though I don't update every gen anyway (or even every two).

Or a credit card ;)