1. Some outlandish policy decisions.
They presented a 10 year programme with a message that it was all doable in one term.
EG - A 4 day week is a fantasy at this stage.
People were scared by some of it.
2. Brexit - Their policy was a joke. Risible. Trying to build a consensus between their educated metropolitan base and their former uneducated base in northern shitholes. Not really working with the former and deffo not working with the latter.
3. They failed to capitalise on Tory ock ups. The tories have run the most dishonest campaign in living memory. Corrupt as fuck. And yet Corbyn has more or less stayed aloof from it, maintaining a dignified silence.
I also think they could have done some deals with the other leftish parties, they all have a price.
But who knows,they may shock us all. We still have a few hours to dream of a better world.
1. I have no objections to setting bold aims.
2. Their base is split, and it's an unenviable task to bridge that divide. Tories face the same predicament, and BoJo fails to take the Remain part of his base into account. I sure have no better ideas how to pull that off than they have.
3. Reasonable people, I guess, can reasonably disagree about the (de-)merits of getting down and dirty with the Tories. I would guess, you have a point here, but also understand the other side.
As to deals with the LibDems, my reading suggests they tried to reach deals with them but failed. There are websites advising voters on strategic voting, rallying behind the most promising left-of-Tory candidate in crucial constituencies. Your "dream of a better world", that is to say, rests on voters' ability to search for, and follow, that advice. Britons are smart people, for the most part. Let's hope they live(d) up to that in their voting decisions.