AI/ML/etc. may be part of it. But the other factor is that you can't just wait 18 months any longer for a new generation of x86 to be a lot [EDIT] faster. That was the big problem with specialized architectures historically. The volume architecture would catch up soon enough without you having to rewrite software to optimize for some different design of processor.

That's no longer the case so specialized designs for the compute-hungry workload du jour (which happens to be AI at the moment) are starting to look a lot more attractive.