Sanders and Corbyn obviously have a lot in common; both are unreconstructed lefties from the 70’s who have succeeded in persuading at least some of the public that their very old fundamentalist ideas are new and fresh. Corbyn won, however, and Sanders won’t. Why the difference?
In a nutshell, Labour voters view Blair and Brown as being sellouts, American puppets, and failures, whereas a large majority of Democrats think the Clinton and Obama presidencies were successes. Anti-establishment politics consequently have a greater cachet in the UK than they do among American social democrats. That is, until Corbyn is viewed as part of the establishment himself, but that will take time.