I think many of you are over-analysing what happened in December. If you live in England then the realistic choices were -
Conservative - standing largely on "getting Brexit done" and spending more on the North of England. Or
Labour - with a huge and complicated manifesto, offering all sorts to just about everyone. An unclear message on Brexit, and no immediacy, and maybe another referendum. Or
LibDem - pledged to ignore the referendum result as though 2016 hadn't happened.
So, in retrospect, it wasn't surprising that a lot of people dismissed the LibDems and Labour because they just wanted an end to the political turmoil over Brexit and to be able to get on with their lives. And, strange as it might seem, a lot of people vote for what they think is the best choice for the country, not just the best choice for themselves. "No one ever went broke overestimating the intelligence of the people" is as good an axiom as there ever was in politics.
Labour's route back to power involves moving the party to the right, abandoning the Islington Intelligentsia, making an unambitious, clear and patently affordable manifesto and dealing with a ton of baggage that they've been hauling around for a decade or more. Keir Starmer's firing of Rebecca LB is a start, but he can't afford to split the party because that'll end in defeat for both versions of Labour. The Covid-19 thing is a godsend to Labour because it gives them a free hit at the Tories every week while the Labour party is in pieces on the garage floor. Every week that goes by shows how inept Boris and co are, and there'll be an inquiry at some point that lays bare how poor the Covid response has been. These are great cards for Keir Starmer. For the time being, I think he's doing the right thing. A few by-elections in the next 12 months might show whether he's on the right path, or whether the public has just had enough of Labour talking a good game but staying unelectable.