> I don't know if it's virtue-signalling, sexual frustration, or something else.

I think de-sensitization [*] may play a big role here; I'm convinced that the more porn you look at, the higher your threshold goes. I've not consumed any porn for years now (as I write in my other comment), and I find the lady in the picture extremely sexual. Yes, she's not suggesting / soliciting / provoking; she is just standing there. I agree. Yet she's no less sexual for that fact.

[*] edited comment for fixing my wrong use of the term