There is a distinction to be made is between a nice guy and a Nice Guy™.
Apparently, there are actual nice guys who, for some reason, are consistently, chronically, long-term unsuccessful in having a relation with a female person, perhaps even being unable to get so much as an occasional date now and then. They are not jerks (that is, those that are jerks are not the ones I’m discussing here), but they have no clue what the problem is.
Even worse, all their so-called friends either have no clue either, or won’t tell them, but simply tell them over and over “You’re a plenty nice guy. There will be someone for you someday, I’m sure of it”. See, e.g., the final statement by kunilou in Post #4 above:
This, it sometimes happens, is a barefaced outright inaccuracy. In fact, it doesn’t always happen that way. For whatever reason, there do seem to be actual “nice guys” who never succeed in having an intimate relation. But all their so-called friends (who would know they are jerks if in fact they are) will never tell them that, but always just tell them what a nice guy they are and promise that they will get a girlfriend someday.
These people eventually will eventually get discouraged with the uninterrupted stream of rejections, disillusioned with the entire tableau of male/female relationships. They may become bitter cynical women-haters, like that guy Loach knows:
When that happens, they have evolved from being a nice guy and a Nice Guy™, and they will then find themselves slandered, denounced, demonized, and considered a creep by everyone – for the unforgivable crime of wanting to have a girlfriend and not being able to get one. ETA: See, e.g., Post #12.