Why do guys feel the compulsion to put his hand up my shirt or sleeve?

I would be watching a movie with the guy I'm seeing and you would think cuddling on the couch is enough. I'm perfectly fine with having my hand rest on his arm with out need to pull up his sleeve in search of skin. But apparently this is what his compulsion is. I was wearing a t-shirt. The lower arm isn't good enough for skin contact? It has to be the upper arm? Same with the waist. I don't feel a need to my hand up his shirt, I am perfectly fine resting my hand over his shirt. But for some reason he has to be resting on skin. Not clothing.

Is this with some guys? Most? Why does it matter? It seems like a step toward something scandolous.
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I'd also like to add, what do guys get out of it? It isn't like guys get a hormonal rush just from touching skin? Or maybe they do? I get the impression it is supposed to 'lead' towards more when a guy puts his hand under clothing, though this guy hasn't been pushing boundaries. I'm also pretty good at 'redirecting' so maybe his intuition tells him 'I can only get away with ___' and doesn't go further even if he wants to.
Why do guys feel the compulsion to put his hand up my shirt or sleeve?
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