Men and women love pretending that the latter are the civilized, non-shallow gender. Plus, women constantly complain about bad boys, players and so on.

Nice guys ought to be a perfect match for them, if we took society's image of women serious. However, women feel there is no attraction. They are unable or unwilling to admit that stability and kindness do not arouse them, especially not when it comes in an average-looking package too. So they rationalize via a twisted version of the sour grapes argument: "nice guys aren't truly nice anyway!"

Add a pinch of generic stereotypes of unattractiveness, e.g. unkempt neckbeard. And boom, women can now chase toxic men, pretending they're the lesser evil instead of the preferred option.

There's one thing women often say that is somewhat right: "nice being the baseline". This is true for women, being treated nicely is the default for women and they're used to it to the point it's dull. For men, especially those of average or below attractiveness, it's completely different. Most of them are invisible and do not receive genuine kindness from non-related people, especially not from women in a romantic context. And heck, many women do not even treat their boyfriend/husband very nicely. Anyway, I've often read stories about how a tiny nice gesture from a woman can make a man's day, week or month even, leading to that man developing oneitis. And a lot of men think that returning the thing that made them so happy makes women happy too, although it's nothing special to them. If there's anything you can blame nice guys for, it's projecting their standards on women.