It's a lot harder to play slowly (and well) than it is to play at breakneck speed. Sadly, that's a fact not widely appreciated by non-musicians, and consequently sometimes exploited by not-so-good musicians.

There are some who are apt to play 'competitively' fast though, and I find that annoying because it so obviously detracts from the musicality of what's happening. It can be fun to do occasionally but I think the entertainment value is soon exhausted.