I think social media icons on porn sites are of limited value -- what are you going to post: Thanks for the good fap!
Do you have a few examples to prove me wrong?
For mainstream websites, affiliate websites or adult industry ''service (B2B)" websites it makes sense.
As for sparse comment or content social media sites, that is a good question, but you have to start somewhere I guess. Some good shilling (ghosting) is being missed ;)