(the thing where men who are already in a relationship are viewed as more attractive by women is actaully true BTW)
it holds true for other things. for example, it's easier to get scouted for a job when you already have one. i think it has to do with heuristics, which are basically mental shortcuts. trying to determine if a person is a good employee/boyfriend/etc. takes time and effort to find out.
however, if said person is already in that position, people just assume that someone else has done the legwork of making sure they're deserving. "he's got a hot gf, he must have redeeming qualities", "she's working at a major company, she must be skilled", stuff like that. in fairness, those statements are probably more likely to be true than not, so it kind of makes sense when you think about it. but it's really all due to human laziness lmao