I'll chime in here that if a person works at Microsoft and has the resources of Microsoft recruiting on their side, that they are in a better position than most to end up with a wide choice of applicants. Microsoft can sponsor visas if need be, and their compensation is generally high enough to merit consideration of relocation, if necessary. (Worth noting here that a non-diverse slate of applicants is in many cases a process smell that your pipeline sucks.)

We also don't know for what role(s) the author was hiring. While the assumption here seems to be that they were having trouble finding a diverse slate of applicants for "Senior AI Researcher, PhD and 20+ years experience required," for all we know they are whining that they couldn't get applicants to be CRUD programmers building out APIs, or PMs, or doc writers, or any of the other myriad roles that go into shipping software. Given that, we don't really know where to place blame. Could be that this manager just sucks at their job.