Momentum didn't exist until after Corbyn won in 2015 though, and didnt play any role in a General Election until 2017. These are fairly simple facts that anyone who actually wanted to have a proper debate about this should be expected to know.
The people who handed us a decade of Tory rule were the people you are praising; Brown was PM at the time.
Are you even from the UK?
Brown done us over when he got caught on camera calling that arl woman a bigot over her discussionon immigration which was a key topic at the time when a few Eastern European nations joined the EU and started to migrate to the UK - he lost the working class vote there and then and played right into the Tories hands.
Follow on from then - Red Ed born with a silver spoon and ultra Liberal Miliband who was as useful as a chocolate fireguard.
Follow that on with Corbyn and his Momentum fanatics handed power to the Tories again.
Whats the central theme? Let the far left take control of the party and naturally then treat the working class with contempt that they are some uneducated gammons that need saving from themselves results in people voting Tory.
Unless you believe the majority actually thought Cameron/May/Johnson were great for the country...