With a few exceptions (e.g. gay rights and immigration), New Labour was to all intents and purposes the Tory party in a red suit.
I posted a lengthy explanation on another thread on why people (or at least young people) are inclined to support Corbyn even despite the clear issues with his credibility and track record. I cba to re-write the whole thing but the essence was: young people are being absolutely screwed over and the electoral system permits them no other choices whatsoever.
I'm still very uncertain about the likelihood of a Corbyn premiership because a) he will have a different opponent next time b) Labour has yet to develop a strategy on Brexit, which could make or break them and c) Corbyn is fairly old and even if he is still around in 2022 might not be well enough to run a premiership.
All that being said, it is not impossible, especially because the govt is so divided over Brexit and has remarkably few talented people who could offer serious opposition.