system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are lefty pitchers normally slower than righty pitchers in baseball?
gpt
There's less competition, is the short answer. You don't need to throw 101 mph to get a roster spot as a left-handed pitcher. Plus, batters don't see lefties as often, so you already have a bit of an advantage and you don't need as much velocity. 

That being said, some lefties do still have high velocity. Clayton Kershaw's 4-seamer averages 94 mph and has touched 99.