What is it with PhDs who ghost?

I just heard from colleagues in a research lab that not too long ago they had a PhD student (fully funded) who stopped showing up to the lab (the PI is quite flexible with WFH so initially it didn't ring any alarms) for a long while, didn't reply to the PI's emails and after the PI threatened to cut off funding...

The guy just kept ghosting? And I read another story in the comments of a thread in this subreddit? How common is this and how can people do it? Like I wouldn't imagine I could ghost my employer to quit even if I wanted to.