I think it's simply social expectations. Single guy is expected to make the first 'move'. Married guy is expected to not make any moves at all. Therefore it's o

I think it's simply social expectations. Single guy is expected to make the first 'move'. Married guy is expected to not make any moves at all. Therefore it's on the woman to begin flirtations with guys who appear to be taken. Married guy concludes he's must be more desirable because women are suddenly flirting with him.