Well technically, the Bible only clearly condemns male homosexuality, in multiple verses in both Testaments. When it comes to female-on-female, there's only a single vague allusion from Paul that's quite open to argument. This differing stance between male and female homosexual activity is possibly due to:

(A) female-on-female sexual activity doesn't entail the same blood and filth that male-on-male penetrative buttsex inevitably does. Thus lesbian activity wouldn't necessarily be considered "unclean" and abominable in the same way that gay male activity was.

and:

(B) widespread acceptance of polygamy (multiple wives) in ancient times; for a multiple-wife family in ancient Hebrew or Greco-Roman society, it would be beneficial if the wives viewed each other as sexual companions with each other for the husband, instead of sexual competitors against each other fighting over him.