"Niceness" as opposed to real kindness is accurately seen as all of false, manipulative, arrogant and creepy. If not consciously, due to all the conflicting cultural messages that seem to encourage the facade, at least subconsciously.

It hints that someone is out of touch enough that they might believe they are entitled to sex because they hide their true feelings as some kind of altruistic gesture. That's mainly the creepy part (that women fear), but also largely the false and manipulative parts too.

The arrogant part is that someone believes they have the power to control other peoples' reactions to them and that people couldn't choose for themselves accurately who they like or are attracted to and act appropriately on those judgments if the "nice guy" didn't attempt to conceal his feelings and beliefs.

Ironically, this last part is actively, and self-defeatingly, encouraged by immature "feminists" who would prefer to only ever have to say yes, because they have an inappropriate reaction to someone positively expressing interest who they don't like. That is, they only want to have men who they are already interested in talk to them (e.g., through a cold approach) and can't reconcile that it's impossible for this to happen without also having to say no to other guys sometimes as well.

Unfortunately, there are so many of these kinds of women these days. They are vocal and have co-opted and abused the visibility that their predecessors worked for and now they dominate the popular discussion through various kinds of coercion.

But, we as men have to give women the benefit of the doubt, assume any given woman is not that kind of person and risk running into one, which is unavoidable, in order to meet those who aren't. Fortunately, they are practically children whose minds haven't kept up with their bodies and the harm they will typically do is negligible, if you protect yourself. Not being able to do so is just one consequence of a lack of confidence.