If you're only being kind to get something out of someone else, you aren't actually kind. And it's not these boys (yes, I use that word intentionally) kindness that is the issue. It's their immaturity, their lack of confidence, their entitlement, their other characteristics that they don't see in themselves that are the issue. It is not evolutionarily functional for women to be primarily attracted to men who are terrible partners. It's a big stupid lie that men tell each other so they don't actually have to do any work on themselves.