In general, people do jobs because they need to earn some money in combination with a sense of enjoying the work. The balance between those goods will be different for each person. I think that people might enjoy the work for a lot of different reasons. They might enjoy having a lot of sex. They might enjoy showing off. They might enjoy the notoriety they find in the work. Some may even enjoy the technical or artistic skill in displaying sex acts for others.
We all know what money does, so I don’t think I need to explain how that might motivate people to do the work.
In addition, in porn, there may be deeper psychological motivations. Supposedly a number of women in porn have been abused. Perhaps men, too, have been sexually abused, and so they might see porn as a way of proving their manliness. Even if they haven’t been abused, they might see porn as a way of expressing power or feeling attractive or of generating some self-esteem—perhaps for the size of their dicks, or for their physiques.
I’d say that in general, the reasons why men work in porn have a lot of commonalities with the reasons why women work in porn. There will be some variation, especially that based on different social trends that affect male and female psychology differently. Certainly male vanity plays a role, just as female vanity also plays a role. Overall, though, I’d have to say there are more similarities in the motivation of men and women in porn than there are differences.