I don't work at a FAANG company, nor have I ever been to SV, nor do I know anyone who works at one of the many enormous tech companies around SV.
In the TV show Silicon Valley they have characters who sit around unassigned doing nothing at the Google-like company in the show. Does this actually happen? Are there people hired at these companies who just don't have a project? Its entirely feasible that Google could afford to do this just to create a dearth of engineers in the area.
Organizational/planning/managerial waste of expensive developer time is real and huge. I'd be surprised if companies the size of Google didn't do similar things some of the time, and if their management's a little more clueful than average they might even make such light-weight or non-assignments official and highly visible to make them easier to account for.