Why are so many fictional female heroes scantily clothed?

I noticed that many female heroes don't wear much clothing: for example, Wonder Woman wears a bikini bottom, when Leia was a slave she had to wear a gold bikini, and Sailor Moon wears a super short skirt. Also, sometimes Cat Woman wears a tight leather suit that doesn't leave much to the imagination. Now, I know that pretty much all heroes, regardless of gender, are good looking, but you don't see Superman or Spiderman saving the day in a speedo, yet female heroes often look like tramps. What gives?