Instead of doubting the intelligence of Reform, and their voters, perhaps it would be better to ask why the two established parties fared so badly?
Until they find out why they did so badly, and convince the electorate that they have changed, Reform will win.
Only because Reform are appealing to the lowest common denominator with low-information voters. They aren't the only alternative party out there.
The real answer to why we are seeing a rise in the hard right is because standards of living are declining - most people are working longer, for less, with a lower stake in capitalism, having seen prosperous times evaporate with the previous generation. Labour have had to cut the nation's cloth to suit and this has contributed to a sense that they must be dealt a bloody nose.
Declining standards of living naturally lead people in all democracies to seek an alternative. In Britain particularly, scapegoating is an effective tactic, because the culture here is one of zero-sum "if someone is getting rich it means someone else is getting poorer" "if a minority earns this right, another group must have lost one" and so on. It's the country of the moat and drawbridge, and the crab bucket.
The main parties are struggling which minority is the one most to blame for why Your Life Sucks (Not YOUR Fault, Median Adult): asylum seekers, immigrants, the disabled, trans people, and Muslims are taking turns at being the Nominated Scapegoat.