A good question, indeed. The usual responses are factionalism, cultism etc. But these answers obscure more than reveal. I think that this questions requires a more serious inquiry into the relationship between ideology and behavior.
My own view is that ideology (and culture in general) is like a garbage can - a repositiory full of diffrenet stuff people put in for various reasons. SDome of that stuff is garbage to some, but can be quite useful to others. It also could be that the same people who see the tuff in the can as either useful or garbage, can change their position id their own circumstances change.
Consequently, people pick up from that garbage can whatever they find useful at the moment, and throw it back in when the picked stuff loses its usefulness.
Stated differently, and more social-scientifically correct, it is not ideology that determines behavior but the other way around - nehavior determining ideology. The Old Man had it right, being determines consciousness.
People picj up ideologies and cultural values that seem appropriate to their own life circustances. Much of leftish ideologies and cults seem appropriate to people who find themselves in a situation when they have nop real power to influence society around them. The adoption of esoteric leftish ideas is what psychologists sometimes call reaction formation - the adoption of views or behaviours to rationalize a negative outcome that is expected to happen.
In other words, it is not that people of Left persuasion are politically marginalised, but the other way around - people who are politically marginalized often adopt leftish cults to rationalize their marginalisation. As soon as their political situation changes, they drop that rationalisation as a hot potato and adopt a more "realistic" (read "pro-establishment") ideology.
These are my 2 cents.
Cheers,
Wojtek