There is nothing you can imagine, no matter how weird, that some men can't use as wank fodder.
I assume the internet is making it worse. Back in the day, top shelf mags were very vanilla, hard porn was difficult to find and a man really had to make an effort to find fetish material. Nowadays lots of men - and boys, let's not forget - are so jaded by porn addiction that they're easy game for streaming sites pushing them towards ever stranger niche fetishes.
It's almost a relief these days to meet a man who's just really into big tits.