One challenge is that when the market stops hiring as aggressively, voluntary attrition retracts as well.

Large companies model attrition in their financials, and those assumptions start to break when macro conditions around the job market shift like that.

That doesn't boost the stock after the announcements, why would they do it?

i dont think this announcement will boost the stock either, for the same reason we are wondering here why 7% is noteworthy for a globocorp.