The actual problem is not them doing those things, the problem is them not doing their job

That's where the demands should lie, not on "bottoms on seats"

Surely being available for work meetings during working hours is part of "doing their job"

Wow, that's insane! My point of view is working at an east coast large research lab, that behavior here would for sure be noticed quickly and eliminated!

In my experience, jammed in an open office in a FAANG, shoulder to shoulder, with people talking loud for hours all around (not enough conference rooms, most do VC meetings from their desks), regular office hours were just for reading email, meetings, looong lunch breaks, loong coffee breaks and BSing with coworkers. Nothing of note got done 9-5 (well, perhaps "team building" did).

Any coding, debugging, thinking had to be done either after 6pm or on weekends, or WFH. Now perhaps you can see why people coast; not everybody is willing to sacrifice nights and weekends to be productive.