The problem you've got is that the general voting population, brainwashed as they are by the Tory Propaganda Machine, find 'the left, the heart and soul of the (Labour) party' very unappealing indeed in terms of attracting their votes.

'The left, the heart and soul of the party' can't win GEs on their own, neither can the entire membership of the Labour Party - they need to get ordinary Joes voting Labour. I'm still seeing and hearing a lot of people who might otherwise vote Labour making excuses for the Tories' abysmal failures over the past thirteen years - "Pandemic, Ukraine, Labour spent all the money and somebody had to pay for it, Rishi's doing his best, yadda feckin' yadda" - so I'm not convinced that, even as the Tories publicly commit Hara-Kiri, Labour are guaranteed to win in 2024.

Id be very interested to hear how 'the left, the heart and soul of the party' plan to persuade voters that a Leftward-leaning Labour Party would be best for the United Kingdom. (Personally, I believe it would, but how are the Daily Heil/Scum/Torygraph/Ex-press readers to be persuaded?).