UKIP was able to drive the Tories right because the 2 main parties were so close in the polls that losing the ~10% of their voters to UKIP would guarantee the Tories would lose a general election.
Labour are predicted to have a 200 seat majority after the next GE. When your majority is that big, it doesn’t matter what a 10% splinter group says or does.
Besides, Reform isn’t eating Labours vote, they’re just going to split the tiny remaining Tory contingent as the old school conservatives move back towards the centre, like every party that loses an election, and the Reform nut jobs go even further right.