I've been in a lot of spaces aimed at lonely men, and I've literally never seen someone say "Why don't women like me? I'm nice!" or "Women don't like me because I'm nice." When I've asked for actual examples, I've been directed to the "niceguys" sub, but that sub is mostly populated by general examples of men being rude or obnoxious. I still haven't seen any examples of someone sincerely being dumbfounded that "niceness" is insufficient to attract women, and/or that their purported niceness is an impediment to attracting women.

In my personal experiences, I've been accused of being a "nice guy" when I point out that toxic men frequently get laid. But "Toxic men are able to get laid" does not imply that I think niceness is sufficient to get laid, or that my own niceness is somehow keeping me single. Calling someone a "Nice guy" in that context makes no sense.

Some cursory googling tells me that "nice guy" first started being used as a pejorative in the mid-90s on Usenet dating communities. It's possible that there were men saying this back then, but that was a long time ago. In the present era, anyone lamenting a "nice guy" is almost certainly attacking a strawman.