Propaganda mostly.

Like look at hispanic trump voters. He campaigned on deporting their family. They voted for him anyway because they want to make it financially, and they have been told that voting Republican is how you do that.

Same with other conservative voters. They vote against their best interests because they are miseducated. They have been told their whole lives that government spending is irresponsible, taxation is theft, immigrants are stealing their jobs, that the Republican party is the party of fiscal responsibility, and that the Democrats are communists (spooky!) who want to make you poor and want to eliminate personal property.

So say Comrade Trump ran on a populist far-left platform. There is no way to really communicate the economic benefits in a way people would understand or believe. They are conditioned against it.

The DSA is attempting this now with folks like Mamdani and El-Sayed. Trying to frame generally left wing economic ideas in terms of "affordability" and making the policies directly applicable to their lived experience. But it is an uphill battle to cut through the conditioning.