First, they are going elsewhere: Lib Dems, Greens. I notice the Lib Dems took another council seat from Labour the other day.
Good. I'm happy with that, and happy with them having a role in a future coalition. If that involves tactical voting to dislodge Tories, great. The stronger they are, the better. The evil Tony Blair had a non aggression pact with the Lib Dems going into the '97 elections. Compare that to the frothing hatred of the Lib Dems coming from Corbynites before the last election.
In fact, the frothing hatred of everyone including swing voters who they might've need to win over. It might not be working but at least Starmer's tried to win over a different constituency. I don't recall Corbyn ever really trying to reach out beyond those who naturally supported him.
Third, the excuses you're making for Starmer re demographics must then presumably also apply to Corbyn.
True - mostly masked in his tenure as leader by a myriad of other incompetencies.
. As for contrition, you're forgetting John McDonnell.
I literally have never heard a Left commentator mention McDonnell and his, seemingly unique on the Left, ability to acknowledge failure. What we get instead, at volume, is a bunch of conspiracy theorising about how the RIght did 'em in and fantasy arithmetic about 2017. You know as well as I do that it's this dominates Left discourse, not consideration of any weaknesses of the failed project and its leader.
In any case, Keith had his "I'm not Jeremy Corbyn" honeymoon period. That he's tanked since is entirely down to him being useless.
And if he continues to bomb in the polls, he'll hopefully go before the next election. I hope the party will have the flexibility and electoral nous to do so. They have more chance of behaving like this now they aren't be led by a small ideological faction desperately trying to cling on.