Why do softball pitchers pitch underhand?

Because they are devious and underhanded people.

@elbanditoroso I knew it.

It’s a rule. And unlike a hardball pitcher, both feet have to be on the pitching rubber at the start of the pitch.

Given that the best softball pitchers can strike out the best hardball hitters, I don’t see it changing any time soon.

Also pitching underhand is WAY easier on the arm/shoulder.

I take it you never threw a softball vs a baseball.
Safety and Health! I played Baseball thru college. Softball in leagues since 20’s.
Getting hit by a ball sucks but softballs can cause so many more issues.
Here is some reading on it