It was an absolute no-win situation for him. I understand why he would have voted leave, because of the imperialist control of the EU, not because he's a racist like the others.
Most of his supporters wanted to remain though, so he had to represent them. I think it's a measure of the man that he campaigned to remain because it was the right thing to do, when it went against his belief.
He could have been a hypocrite, but that's not the kind of person he is.
He would have implemented brexit immediately, and he would have been the perfect person to do it, because it would have been for the right reasons, bringing control back to britain... not just about immigration. And I'm a remainder.
Keir proved time and time again that he is far from a decent man. He lied and manipulated to get to where he is... and he continues to purge the party of those who even mildly disagree with him... particularly women of colour.
Corbyn managed to inspire the youth and get them talking about politics. Keir destroyed that and his work will take generations to undo.