The reason for going to Apps versus the controller is pretty easy, it is a lot cheaper to support an App on a phone or tablet or computer. If there is an issue with the app, it can be updated (patch) pretty easily, user downloads a fixed version. Yeah, there is testing to make sure it works on various devices (IOS, Android, PCs, phone vs tablet), but these days with automation that actually isn't that big a deal. You want to add a new feature, it is pretty easy to add it to the app.
A physical controller has a lot of disadvantages:
1)Can break physically, buttons break, circuit board breaks, etc.
2)It is manufactured, so you need to have the unit made, you need to have tooling, and of course these days the shipping/supply chain.
3)If there is a problem with the unit, if it is a software issue the firmware in the unit may or may not be able to be upgraded (why they wouldn't have it all upgradeable, I don't know). If it is non programmable firmware involved, has to be swapped out.
If it is hardware, then there is the fun of parts, if a button goes, if a display screen goes, it is a pain to fix it (yeah, a phone or tablet can break, too, but then again, those are mass produced items that can be fixed or replaced easily. If your tablet breaks, you can use a phone until it gets repaired or likely replaced).
4)You have to have a repair service, at least for warrantee work,or have extras on hand to replace broken ones.
That doesn't mean I think there shouldn't be controllers (not so sure how much I'll like using an app), but why they are doing what they are as makers.