When someone starts a site they are likely to look for a designer and ask to see a portfolio of their adult work. Given the nature of hiring designers for adult and non-adult, they're likely to want to hire someone who has a proven history of reliability. Given the nature of adult, they're unlikely to approach a non-adult designer. After working through all those barriers, they're then left with a relatively small group of designers who have been doing the same shit year after year after year.
__________________
|