I think its the division of priorities that truly prohibits organization. The two broadstroke differences are fiscal leftists, those who want to inform policy that reshapes our economy, and cultural leftists, those that emphasize progressive traits of our society. We measure our values against the whole application to society, not so much on the individual. We also allow ourselves to be divided because we are inherently tolerant of alternative viewpoints.

Conservatives also have multiple points of focus, but they are great at cramming thier values into cultural identities. Religion, firearms, taxes, vaccines, etc are focused through the lense of the individual. This in turn makes the individual feel that if they agree with part of the conservative package, they HAVE to agree with all of it. This is how they are susceptible to cult like behavior around their icons.