Reform support is too broad geographically and demographically that Farage has very little chance of being the next PM, unless the UK changes from FPTP. They take votes away from the Conservatives much more than they do Labour. This is why Cameron and Boris both buckled to UKIP/BrexitParty/Reform, but Starmer doesn't need to.

FPTP also benefits parties with strong regional hotspots, such as Labour in cities.