I see what you're saying and I had a similar thought when I found out Anastasia Blue had passed away after I had... you know...
But it's really not as weird as you think when you analyse it. (I was going to put 'dissect it' but the word 'dissect' in conjunction with talk of dead people has unsavoury connotations).
The thing is, like several other posters have pointed out, people still enjoy the works of people who are dead whether it's Shakespeare, Hitchcock, or whoever the fuck.
...I know, I know, the difference is that you're appreciating their work not their physicality but the principle is the same. A porn star's films
ARE their work.
Let's take a non-porn example: Audrey Hepburn. She's hot, but maybe you think that's different because she was popular decades ago and so to you it's an issue of being 'too soon'. But unless they were ashamed to be in the adult film industry then I imagine most porn stars would absolutely love to be considered wank-overable for generations to cum
However, if you've just found out they're dead and
that's the thing that turns you on then, yes, maybe that's a little weird.