And they may make enough and have enough savings that they care less about a salary bump. They probably own a house and don't want to move for any number of reasons--which still matters a lot of the time even in this more WFH friendly world. And, at some point, they know that a job search is probably going to be harder. And there's always risk with a new job.

I've certainly known people who would entertain a move if a new position fell in their lap but wouldn't likely seek one out.