Sex is enjoyable

SO many different factors: abuse, traumatic event, sexual abuse, environment, peers/family, etc. It can be anything that caused them to think that being that way is the only form of "love" they can give or receive.

Variety is the spice of life.
*plays Spice Girls song*

hormones? No...there are lots of reasons...one common one is that many promiscuous people were raped and or molested at some point in their lives...particularly women. Whatever, they got bad messages about sex, it's meaning and consequences

Fun loving,confident and sexually liberated.

feeling need for fresh sexual experience and orgasm.
feeling need to be wanted and needed by men
to prove myself that I attractive for men

lack of discipline and self control

Maybe they enjoy the game but are too afraid to bond.

An pervy uncle doesn't help

Being human.

Liberalism

They may just want to experience a lot of sex with a lot of different people. Might be no more complicated than that.