Like stated before, most adult website owners are average joes, and PHP being easy to learn with a low entry barrier it was the logical reason to get a site up and running fast. Also because many of the tools written for the adult industry were done in PHP. Just like ICQ it won't ever be replaced as the standard for the industry.
From what I recall its essentially how people do business. Everything from technical support with adult oriented hosting companies to making deals to sell sites/traffic/etc or talking to sponsors about promotions/etc. Plus a great deal of just general bs-ing. You have to remember outside of maybe a dozen large companies, most adult sites are just run by 1 or 2 guys so its their form of talking at the water cooler.
Basically this... And so many old school peddlers have stuck with ICQ and it's just easier for them to keep using it instead of adopting a new modern form of instant messaging.
