When you quite clearly treat another woman differently from another woman, being overly kind, in the hopes that she’ll show interest in you. Not politeness.
Men traditionally need to be providers for women- it’s a masculine trait. Any man who refuses to is not masculine and thus unattractive. Very much a turn off.
When you’re overly nice to a particular woman compared to others… It comes off as desperate. In the least it comes off as if you’re romantically interested.
I think it’s because we can sense it’s often because the guy wants something more than just friendship, and we’re not attracted to that particular person/are in relationships