I've known 2 SP's in my time who did it because they really loved sex. Both were full out swingers who viewed sex like drinking a glass of water. In both cases their husbands were their security and drivers. Down the middle most of it was because they had kids to pay for, they needed money & they didn't have a lot of job opportunities and it offered flexible hours. On the ugly side of things I was a driver for a woman for a short period of time who would come out of the session & cry in the car. She didn't make 3 months. The industry can have a huge emotional toll on a woman.