Like Rocky Anderson and the People Party, ego’s get in the way of pragmatism.
Well it's the concept of power. For the main parties, unless you're Donald Trump or Bernie Sanders, you're required to compromise to climb the flag pole and achieve power which is the point of politics. Once you've decided you're not going to be a member of one of the main parties' power structure, the incentive to compromise on anything disappears. Because compromising and having no power is the same as compromising and likewise having no power.
One reason for the heavily splintered left: cohesion requires them to all agree with one another - i.e. compromise. Even if you have all left-wingers or all right-wingers in a room together, you're still going to be required to compromise for the group to work. The only other option is you have a dictator in charge or a "politboro" running affairs.
haha, how's Bernie's Medicare-for-All push going these days? I agree with the point you're making, but I'd go even further and say that there are no prominent exceptions, not even Sanders or Trump. Even prior to 2016, despite the rhetoric Sanders behaved like a normal Senator making pragmatic deals and votes to advance his goals--and he's certainly leaned into the horse trading since losing to Biden. And even Trump "compromised" on his promises not to attack the social safety net or continue our pointless wars--the policies he actually pursued in office were Obamacare repeal, regressive tax cuts, and support for foreign autocrats. Oh, and filling the federal judiciary with activist judges committed to crushing individuals' and workers' rights. Basically, he adopted the traditional Republican agenda in exchange for party support.
