I can think of several reasons...
If he was her boyfriend, they may have simply broken up. It happens often, and more often in couples where the girl is dedicated to sex. In the end it's not a stable relationship or tied to anything.
Another reason is very typical: videos stop being interesting because fans get bored of always the same, and ask for more. Then, to maintain the income or grow in the business, sex business girls looks for ways to do it with other guys. They do not usually explain the reasons, of course. But money is an important one.
Watch out: it's not easy to find a guy to shoot porn videos with who perform and look fine on camera, that offers chemistry with the girl, and that has experience in how to fuck like a porn actor.
There's nothing worse than looking for another guy to fuck other than the bf, and making videos that looks crappy and poor. Not all guys are good for porn.
With married sex girls I think it is similar, just more complex to negotiate and manage among the couple… because their relationship is much closer than a simple boyfriend or partner. Getting married and becoming parents is supposed to involve certain things that having a boyfriend does not.
If you look the comments MissLexa always gets at PH, the most popular ones (other than her showing her face) are requests like fucking a black cock, fucking with three guys, getting fucked in the ass by two guys, and even more hardcore stuff (gangbangs,...). People want more and more. And one way or another, to stay in business they have to innovate. That's why they always end up resorting to fucking other guys.
She has hundreds of videos with her husband, all good but also very similar. And since neither of them show their faces, they are even more monotonous and repetitive. They know it. That's why they turned to other men to make MMF (Tony and the fan raffles). It's a matter of business.
