Letting people work at a slow pace for a while, PIPing them, then ultimately firing, is very expensive. An unproductive teammate not only doesn't get stuff done but also brings down the rest of the team.
Edit: Some companies also don't like the morale effects of sink-or-swim, though Amazon is fine with it I've heard.
They aren't exactly bad hires. Lots of previously solid employees were going kinda AWOL sometimes while remote. Even if someone wants to be responsive, after seeing enough pings go unanswered all day, they might follow suit.
They could redefine the job requirements to be remote-first, but that'd require a lot of firing and hiring.
Edit: Some companies also don't like the morale effects of sink-or-swim, though Amazon is fine with it I've heard.