Let's assume they aren't lacking in brains nor perception.
They know he's a Tory.
They know he's a fawning establishment lackey.
They know he won't do anything slightly leftish at all.
They know in fact he will do the opposite and play the "muscular" card on Foreign Policy, Defense...Social security...etc... to out-Tory the Tories which can only mean that they are aware that ordinary peoples lives will get worse under Starmer.
Yet...on the "positive" side they will get the cachet and self congratulations of voting for what they can pretend is a moderate progressive left wing government. And if you bring it up the fact that its not they will give you TINOATORY: but "...There is no other alternative to the Tories."
It's a win-win in middle class circles: what's not to like?