I'm aro/ace and not dating, but my circle of friends is progressive and most have become poly over the last 5 years.
So I'm acquainted with probably +25 poly guys, most of whom skew progressive (but there are a few who lean more libertarian in there too, and a couple anarchists), and am good enough friends with probably 5 progressive poly guys to have a good sense what they have learned, how they treat their partners, and what their partners find appealing.
To be fair, to me polyamory looks like an insane amount of effort for the payoff - bc I am not interested in even one relationship let alone the intense effort of managing multiple. But from what I have seen, successfully being poly means learning a ton about boundaries, communication, and maintaining respect because all parties constantly have to manage jealousy and limited attention each of their partners. If you don't respect one partner - poof!! -- that relationship is over. And your other partners will likely hear about it, in detail, from both sides and litigate it bc they have a stake both in you and in being someone with you. It is a ton of drama.
But it also seems to be a crucible for learning how to negotiating needs and figuring out how to talk about it openly with each other to build connection - and that process both requires and builds respect for your partners.
Like I said, the guys I know who have stuck with it and learned the necessary people skills now have the problem of having too much interest. Including one friend who had terrible luck dating before and who I worried was on the verge of becoming an incel. Then he dated one of my first friends who was poly, and she kind of taught him in no uncertain terms how this works. Between that and his next poly girlfriend, I watched him become someone who is deeply considerate of his partners and is also confident about his boundaries and what he can offer. He's got like 4 relationships going on, 2 of which are long term.
And again - the biggest change I saw in him was that he stopped seeing the women he wanted to date as games to win or challenges to overcome, and stopped carrying the frustration and shame that comes with the 'failure' to 'score'. He still looks at women with clear desire, but that desire doesn't make him feel like he has to be manipulative or play games.
I don't know how to explain it except that he has a respect for the women he courts that most single guys do not. Maybe it's that he has less to fear from rejection, so he doesn't have to mentally dehumanize women as a coping mechanism. And this is a feature I see in most poly men, and have seen emerge in men as they fall into poly.
Actually - I'm going to ponder the 'able to respect women more bc they have less to fear from rejection' idea more, personally.
That alone may be a big part of their appeal, because a lot of the threat that women have to navigate when being courted is how to safely disengage if a promising flirtation turns sour. There is a lot more enthusiasm to explore or move fast when you are free to say no without fear of a possibly violent meltdown.
And poly guys aren't going to meltdown. They are ok with a no, they are emotionally braced for that and have been through worse feelings already. And they have other relationships to fall back on.
Oh no. Ohhhh no.
It's simply what consequences are dished out for.
This is mob rule government. If you are part of the 'gang', and are loyal to the gang, you can get away with murder. Or raping children.
Everyone else is under the bootheel though.