Why would a girl dry hump but not kiss?

The girl I've been going out with for a while won't kiss me because she says she believes it will complicate things and/or doesn't see a future for us. But just the other day she initiated cuddling and literally dry humped me. I started kissing her passionately and even though I could tell she enjoyed it she never returned the action. What am I missing here?
Why would a girl dry hump but not kiss?
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