Outside of school where friends basically just enjoyed each others company, I would say most friendships now are made in the work related environments so there is often a layer of politics involved that make it difficult for everyone to see who is sincere and who is just networking. Nobody knows how they stand with each other so they are hesitant to develop strong relationships and trust with others.

Traditionally these bonds came about through other things like neighbors, communities and religion, but people are constantly moving for work, and society is more pluralistic (and secular) than ever so most don't begin to lay roots until they have a spouse in these roots aren't being laid, and there hasn't really been anything new that fills that gap outside of where you work.