The reason is obvious: The left hates us and what they claim to stand for is irrelevant, only what they actually put into action matters.
Every side will claim to be the representative of "good", but what you can actually say and do while remaining part of the in-group is a far better indicator of (revealed) preference than any political manifesto. By that metric, the left mostly stands for identity politics, where men are inherently evil and inferior.
I still think the left is a better bet than the right, but I can see why most incels would feel doubtful about that. And why many of us hate "the left" with a passion. These status-seeking, emotionally incontinent, amoral vermin that fill much of higher education and have migrated to the left for the same reason they would have applauded the burning of witches or lynching of blacks in the past. They are driftwood, they don't care enough to have "a side". The winning side is their side. The left is winning, so most of the worthless mid-wits are on the left.
No good idea survives the contact with the average citizen, although that might be unfair, the real drive towards this insanity might come from the top, where power is centralized. Doesn't really matter in the end if it's people overall being shit, the most influential people being shit, or both. Is the west running it down because we are innately self-flagellating Christians at heart / inside our genome, or is the western elite running it down because adding women to the workforce and importing migrants allows you to cheat democracy, drop the price of labor and keep population above replacement without needing to address the issues underlying the fertility crisis?
In the end, the core moral virtues of the right simply don't align with our interests. Is what I would claim. The right cares about winners. And we are born losers. They don't care about our plight, they only want to use our misfortune for their own interests. That is true about redpill gurus, all the Islamists, all the other religious groups, Nazis, the trads, the Republicans, the NRx, all of them. Men and male group-interests are never at the core of their agenda.
There is the men's rights side of things, but I think it's clear that what we represent is at most a fringe sub-section. We are much more focused on the sexual market, rather than anything else. After you have food and a roof to sleep under, what really matters most for your overall happiness is your social life, your romantic life being the most important part of that. MRAs are usually still beholden to many Feminists ideas which simply either aren't true or are incompatible with men striving for equality in the sexual domain.
So really, our movement hasn't been born yet. It might originate in something that already exists today, but it will require some fundamental change to occur, because right now we are alone, isolated and despised. We justifiably hate and revile the society that abandoned us to live lives not worth living. While it claims equality and even equity as its core values, it leaves us to struggle in vain on our own for an ounce of love, affection or intimacy simply because of the bodies and sex we were born into.
I would side with anyone, be it right or left, religious or aliens from fucking mars if that side could convince me men as a collective would flourish under its influence.