It's mostly Tory voters who've moved to Reform, not Labour.
Lots of Tory voters were small business owners, tradesmen, self employed, etc., for whom Labour don't represent them anymore, now Labour have shifted to being the party of the unionised workforce rather than all workers.
Sunak screwed over 3 million small businesses, freelancers, tradesmen etc with his ridiculous covid support exclusions, so that's 3 million votes that Tories lost to Reform in 2024 as those excluded would never vote for Sunak!
Tories also appeal to OAPs, other non unionised workforces etc (staff in small businesses etc).
Labour's core support is now public sector workers and heavily unionised workforces (mostly public sector), and those who've retired from public sector.
They're really not been the party of choice for other workers for a long time.