Because you might not fit in "culturally". Which is BS. I've noticed that going to work for many, primarily younger, people is more a social thing than a professional one. I see lots of time spent talking about and focusing on what people did in the 16 or so hours since they last saw each other at work. Mondays are the worst as sometimes an hour or more is blown catching up on what everyone did over the weekend. People and teams are lacking direction and focus. These younger teams need stronger leaders able to focus and re focus the culture and discussions on achieving organizational goals. These "work is social" folks fear those who might make them look bad by focusing on Getting Shit Done rather than focusing on people's personal lives. This isn't to say we shouldn't care about people and their lives outside of work, we should be empathetic, but it shouldn't be what the team gels around.