Most other ARM implementations are terrible. Say what you want about Apple's business practices but their processors are at least several generations ahead of their competitors.

Other companies have been trying to "make and improve RISC processors" for over a decade now that ARM processors have exploded in popularity, turns out most of them just suck at it.

We'll have to see about RISC-V but until companies start making processors that are actually competitive performance wise, it won't catch on.

Apple has always reserved its processors for itself, so unless Apple suddenly starts selling its processors its not going to singlehandedly lead to the collapse of x86