Sure, but I don't think it's usually the apps that people pay much money for. And on top of that, app store revenue is (from a rough estimation) 6-7% of total revenue (although it's high-margin). Apple would be entirely fine.
And if you're right that the phone of the future will be reimagined as centred around being an AI assistant: innovative device design, user experience, hiding technology, integrating software/hardware/cloud are all things that Apple is historically pretty good at (with hiccups and bad periods for sure, but other companies certainly aren't better in general).
~15-20% of Apple's total profits at ~75% margin.
Investors are not going to like if that suddenly starts shrinking.
all things that Apple is historically pretty good at
Not to mention, Apple is going to want to not disrupt itself so they're going to deliberately slow down which opens up the opportunity for someone else.