That's not really true at all. Republican voters are the ones who wanted - and demanded - to have Trump as the nominee. Many establishment figures in the RNC did not want him. However, if they had taken steps to deny him the nomination, there's a very real chance that he would have run third party and split the vote, which he threatened to do several times. Hell, his supporters showed up to the 2016 convention armed and in numbers, in part in case the establishment tried something last minute.

On the Democrats' side, the DNC have basically hand-picked establishment candidates for the past three elections, and they do it because they expect people to bend the knee and fall in line behind the lesser evil. Bernie was never going to run third party, and his supporters were never going to show up with guns at the convention. He actively campaigned for Hilary and they still blamed him, even though the number of Bernie-Trump voters was much smaller than the number of Clinton-McCain ones, and Clinton sure as hell didn't stump for Barack.

If Republicans are more loyal to the Republican party, it's because the party responded to what they wanted. And the reason that they did so is because the "my way or the highway" mentality is so much more prevalent on the right. Liberals cannot ever shut up about the "lesser evil" and making the "rational" choice, while Conservatives don't give a fuck about that shit. Conservatives don't masturbate over how they're so rational that they'll humbly accept things they find morally abhorrent in order to prevent a greater evil the way liberals do, they say, "You can take my guns out of my cold dead hands," and their politicians listen to those red lines, at least to a degree.

Meanwhile, establishment Democrats have an actively hostile relationship with the left, and liberals still demand that we support them unconditionally.

I disagree. Not about the party loyalty to republicans but to the idea that people drop leaders for some perceived purity test.
I think it is a useful myth that excuses the behavior without looking into it more.

People want leaders that support and help them the individual. We are focusing on social ideology instead of financial which is the primary driving factor for Republican voters too. They are just more communal and expect members of their perceived community to be helpful to them and are taught to leave it to a higher power to solve.

Anyways, the Democratic party is not picking policy that is big tent. They are picking stuff that is hyper specific sub groups based on cultural aspects and invites awareness of whether you are in or not. It makes it appear fractured cause we are rallied as sub cultures under a fiscal conservative umbrella. If the policies were pushed as supporting the financially underserved it would be easier to recognize yourself as belonging but it would impact the financial support of billionaires which the party actually courts.

It appears we can't win cause we are trying to play the same policies the republicans do under a guise of social structures need to be fixed instead of financial ones. Push for policies that are big tent and makes it easy to the average person to see them belonging in (poor) and thr support will come but the policies will need to change to. So which comes first?
It needs to be politicians cause no one will trust to elect the other way around.