Out of purdah now so can comment. Labour's problem is that the old notion of "the working class" ended when Thatcher got elected in 1979. Those people, who would normally turn out to vote in droves for the Labour Party, suddenly found they could own their own houses, cars, go on foreign holidays, own shares, get credit easily, etc. And suddenly they were more bothered about things like exchange and interest rates. People had money in their pockets and lots of things to spend it on.
I remember Michael Foot promising "exciting politics" just before that disastrous GE under his leadership. He and Benn had interesting things to say but most voters really didn't care about "exciting politics". They wanted good, well-paid jobs, a good standard of living but something to fall back on if they had a problem. Whatever you think of Blair and Brown, they understood that.
I've said before on this forum that had Corbyn kept to a few, simple but radical ideas, that had an impact on a wide range of people, he might have won power. Just promising to make the tax system fairer and nationalise the railways might well have done it. Shame he was an antisemite and a friend of antisemites as well, which didn't help, plus he went way over the top with far too many policies, some of which people found threatening.
You can't campaign in the 21st century on policies that wouldn't be out of place in the 1960's and 1970's. The world has moved on. If you want power, you need to appeal to at least 40% of the current electorate, which is enough to get you elected. I've no idea who Starmer is appealing to at the moment.