As someone who has been in many, many MMORP communities throughout the twenty+ years I've been playing them, I can answer this with certainty.

RPers are often the second people in PF to get the new glams, hairstyles, and fashion accessories right behind the hardcore raiders (there's also decent crossover), but unlike the hardcore raiders who leave once they've exhausted their content for the patch, RPers stay and make their own content.

They are more likely to dump money on cosmetics because cosmetics are half the point. Yes, you can use Glamourer to ape the items, but people know that people without Mare couldn't see the items if you weren't actually wearing it, so you'd acquire the paid items anyway.

I also know that when you chase away your RP community, your MMO is in a lot of trouble.

When content dries up, when games go into maintenance mode, when the servers are ten minutes from shutdown, the only constant is that your RPers are the ones still there. Chase them off and you lose a ton of easy, secure, and stable income.