I've always thought not being friends with your coworkers is a defense mechanism. Most of us have to work to survive, so getting emotionally involved and ending up with an uncomfortable or toxic environment (one with conflict and favoritism) is a big risk.
I've observed that the more highly paid and "professional" your work environment, the harder it is to make friends through work.
I've observed that the more highly paid and "professional" your work environment, the harder it is to make friends through work.