Theory on why the left is doing so poorly

I was watching an attack ad against the government this morning, and it struck me just how useless it was going to be.

The key focus of the clip was on homelessness and food banks, with a little on the NHS. Then I thought of how someone like my dad would see that video. I mean, he's not exactly a labour swing voter, but he would swing between Cons, UKIP and independents, and isn't completely against Labour, under certain circumstances. He would look at that, and think, yeah shame about those people, but that's not going to change my vote.

If you follow Haidt's moral foundations theory, the left care most about fairness and harm, and little about anything else. It seems their tactic is to just keep highlighting how nasty the tories are, in the hopes that everyone will eventually agree that they're too nasty to vote for.

This is good as an element of the overall strategy. However, the left seem to have become completely obsessed with this, and want to rely on it wholly and keep trying to drive up the outrage at the expense of caring about anything else, and they're just not going to get through to people.

Moreover, they seem completely incapable of realising that other people care about other things, and some seem to think that they don't even want the votes of people who are too heartless to care about homelessness and food banks

It's endemic among the corbynite left, and I don't see it changing.

Thoughts?