It is possible this girl is looking for a relationship that is not based on sex. If she is doing all day, she mightn't enjoy having to continue into the night.
I've asked a few MLs about their boyfriends, and the attitude is usually they don't want boyfriends for this very reason. Maybe out of embarrassment from having to explain their job, though?
I've been "dating" an ML for a few years, we meet up for lunch about once per month, and usually end up at her place for a massage session which I pay for. We are great friends, I help her with her business but we are both committed singles. We are not going to spoil the arrangement with free sex. She has her customers, I see other MLs as well.