There are plenty of problems with the standard Nice Guy story like male entitlement, misogyny, etc. but I want to focus on the word nice itself and how it relates to people describing themselves and others. Somehow people seem to have become desperately confused about what Nice means. Sometimes it means "Lacking a particular negative trait" and sometimes "Nothing worth remarking on." It never means "Super awesome sexy person." When a guy describes himself as a Nice Guy what comes across is that he looked for actual complimentary things to say about himself and came up empty. I can hardly imagine a greater condemnation of yourself than an outright admission that you have literally nothing to say about yourself. If you describe yourself as a Nice Guy you are simply stating that you are in fact a Nothing Guy. Is it really any surprise that other people aren't interested?
Really, what is required to be able to call yourself a Nice Guy anyway? You haven't stabbed anybody this week? There isn't an arrest warrant currently out on you? You don't randomly punch clowns? These things aren't much of a bar to clear and even then there are plenty of dudes who can't even make all of them who consider themselves Nice Guys. Being in the top 95% of the population in terms of not being a violent criminal is hardly a compelling argument.
The same goes for straight women talking about how they want a Nice Guy to date. They don't actually want this because Nothing Guys aren't appealing. They might want a hot guy, a funny guy, a guy who loves wine tasting, or a guy who can recite Star Trek episodes but they sure as hell don't want a Nothing Guy. If a woman says to her male friend that all the guys she dates are terrible and she wants a Nice Guy she is simply indicating that she wants someone who is appealing like the guys she dates but who lacks some deep flaw those other guys tend to have. She is *not* saying that she will happily date anyone who is inoffensive.
If a dude has nothing more to recommend a relationship aside from being horny and a reputation for blandness then it should come as no surprise that he is lonely. I still have sympathy for the pain of that loneliness (I have been there, I get it) but that sympathy does not imply that the world is being unfair and owes Nice Guys something more. Being a Nice Guy isn't a badge of honour, it is an admission of being boring. We all know that people choose friends, dates, and mates on the basis of physical attraction, intelligence, passion, humour, shared interests, and a host of other factors. Being Nice does not feature prominently on that list - assholes still seem to have plenty of people happy to be around them as long as they are interesting.
I am imagining what would happen if women in these situations articulated their desires differently. If all of those "My boyfriend is such a jerk, not like you, you are my best friend and always listen when this happens" conversations ended with "And I really want a guy who is a super dancer, owns a yacht, has six pack abs and brings me bacon in bed" rather than "And I really want a Nice Guy" then things might go better. It wouldn't get those two friends into a relationship but it would at least make it clear to the Nice Guy why he really ought to go move on to somebody who actually wants him. On the other hand making such statements is hard as it requires knowing what you want and puts you very much at risk of having your desires criticized. It is hard to argue with wanting someone Nice but people will be happy to nitpick a desire for a fancy job.
On the other hand it would also be easier if Nice Guys would hit on women who actually want to date them of their own accord. Stop with the whining, cease waiting around for someone who obviously doesn't want you, and get out there to find a relationship with somebody else. If you truly can't think of anything else to say about yourself other than Nice then that itself is the problem. Practice singing and playing guitar. Develop an incredible passion for Greco-Roman wrestling. Hit the gym and try to get those six pack abs. Read a bunch of ancient French literature. Just find something that will let you answer the question "So, what do you do?" with something exciting that gets you stoked. Maybe the person in question isn't impressed by encyclopaedic knowledge of wildflowers in particular but being "That guy that knows a ton about plants" is infinitely better than "Nice Guy". At least you won't be instantly forgotten!
Convincing people to stop using the word Nice when they mean Nothing wouldn't stop all the Nice Guys from being sad and lonely. It also wouldn't prevent the associated bitterness towards women and confusion as to what could be done to actually fix the problem. However, it certainly couldn't hurt and it seems like it might help. The benchmark for being attractive to others isn't some nebulous lack of obvious offensiveness but rather being interesting and I think right now language is actually part of the problem.