It's going to depend.
In my own case, I opted not to go with a poly married woman because I am single, want a life partner of my own, and am realizing that I need to honor my desire for a life partner.
It doesn't mean that I won't potentially have additional partners in the future.
It does mean however that I am finding it very triggering to attempt to be involved with someone who is partnered when I am not. It was easier to avoid the situation than to deal with my own feelings of envy and sadness, and triggering of deep childhood wounds ("I am always left out" kind of feelings). It's ideal to deal with your feelings - but sometimes avoiding drama is much, much easier. I also felt some feelings of being "one down".
It also means that I want to put my energy into dating to meet potential life partners, not into this relationship.
But the thing with poly culture that's easier to deal with, is that she and I are becoming very good friends. In monogamous culture, there would've been more social pressure to either couple up or not.