The reason why pure math is the easiest field for AI is the same reason pure math is the easiest field for one person sitting down with pencil and paper - an entirely theoretical field with closed, bounded, deterministic logic whose problems can be addressed by pure thought without needing to survive contact with the lab.
While very impressive, it says little to nothing about the real world that has open, messy, non-deterministic problems with sparse data that have hard experimental verification and barriers.
The fact that so many are wildly extrapolating from the Navier-Stokes equations to all kinds of applied fields says little about what AI can actually do in those fields and everything about the awe with which society sees math and mathematicians (I share that awe). It’s about psychology, not technology.