It all depends on whether they want to win a general election or not. You can have all the principles, ideals, ideas and policies you wish, but if you don't appeal to the "middle ground" and get Tory and Lib Dem voters to vote for you once, you won't win an election, simple as that. The Labour party has changed direction, and headed left, left and left again. Most Labour MP's now do not agree with Corbyn's personal views, that's clear. That's because a lot of them have their head screwed on, and recognise that however much Blair is hated and despised by Corbyn and his clan, he was the most successful Labour PM and won 3 elections for Labour. What's the point of having all the lefty ideas only to sit in permanent opposition and never get a chance to change anything?
Take Blair out of the equation, and we're back to 1974 when "Old" Labour last won a General Election. The truth is that Corbyn is much more comfortable in opposition, he's great at protesting, but would crap himself if he actually had power handed to him. Best thing to happen is for him to continue his bullying and purging, and keep the Labour party split up the middle, and well away from power.