I've heard of very few conversations with 'should be' labour voters that suggested that going back to Blairite-Miliband-esque economic policies would be what would get them to vote Labour - the problem was overwhelmingly the london-based swing to remain and Corbyn personally.
From where I sit it looked like fairly obvious, Politics 101 stuff - accept the referendum result, and don't ask people to vote for a bloke who went on cycling holidays in East Germany, was best mates with Gerry Adams, and who, through his odd friendships and bizarre tastes in art, allowed himself to painted as anti-Semitic.
Corbynite economics were almost universally popular - and not just amongst would-be Labour motors - but the move away from respecting the vote, and the man personally, was electoral poison on the doorstep.