The reason is honestly painfully simple; A lot of people on the left seem to be obsessed with the idea of being "on the right side of history", while the right is concerned with being on the right side of your community.

It creates this interesting dynamic where a good portion of left wing people can only look at conservatives as some kind of historical enemy with whom you share a fucking feud. Conservatives look at it differently; if you are part of the community and aren't actively try to subvert or destroy it, it is necessary for you to defend them and try to get along with them. Being a subversive is the cardinal sin for a conservative. Being regressive is the cardinal sin for a progressive.

We do not care if history judges us harshly, for those in history do not live when we do. They look at us from an ivory tower of moral development, much like we look at the past century from an ivory tower of moral development. No doubt, many conservative AND leftists ideals will be considered to have been on the wrong side of history. But why give a shit. You don't know who is going to write this history, you don't know if you have reason to fucking like them. There is no need for some kind of absurd moral drive where you try to read the social trends throughout history and base your beliefs on wanting to be defensible to people 90 years down the line.

And ultimately, you might be in the contemporary equivalent civil rights movement, to be lauded for centuries to come, or you might be the contemporary french revolution; being lauded before taking a massive L and somehow resurrecting the monarchy through sheer malicious incompetence. Just do right to your community.