My best guess is a mix of bad investments in commercial real estate (similar to 2008 regular real estate) an increase in political activism, because people are realizing they can have lives outside work, increased unionization efforts, etc. All of which come with people having more time for themselves and being less directly influenced by "company culture" when they are in an office.
I doubt it has anything to do with productivity at all. Just harder to really influence and control people if they aren't forced to be where you need them to be to do so.