Why is arrogance and egotism a (seemingly) common side effect of high intelligence?

Whenever you read in detail about great thinkers or scientists (even philosophers), trying to get into the nuances of their lives, you always come across instances of them being conceits who let their self-importance go to them. Sometimes being outright abusive to whoever's nearby, or anything that isolates them from others (sometimes deliberately), or engaging in abnormal or downright repulsive behaviours. These are always a recurring theme among great thinkers.

You think they would know better.