it’s baffled me for three decades

They’re either racist, hold some other form of prejudice or they’re hypocrites.

They’re bad people. I’m sorry if they’re close to you but they’re bad people.

I get it, I have a relative like this. Their flaw is racism and prejudice toward LGBT+, so they support and vote for awful politicians.

I think you have pinpointed the core issue.

Right-wing republican policies and ideas lends themselves to simple (but often wrong) models of explanation; "it is the fault of the immigrants; the poor; abortion is always immoral", etc. You get candidates that radiate confident leadership spewing simple talking points they believe in.

Left-wing, especially progressive, ideas are often rooted in insight into the incomplete understanding we have of the underlying complexities. People who navigate these ideas won't be as confident: "the cause is a bit of this and a bit of that; we don't really know, but research points at" etc. To confidently sell policies based on these ideas to voters requires a level of cognitive dissonance, and also opens for criticism on being indecisive.

How can we package left-wing ideas in a way that attracts voters who are swayed by simple ideas presented with absolut confidence?

Yeah and I think I fall for this somewhat too. Here in Massachusetts we tend to be fairly progressive but tend to elect Republicans governors, because they’re more “leadership”.

Even among presidents, I didn’t hate Reagan as much because at least he was “presidential”, not embarrassing as the public face of the country, but then we had ever shrinking republicans that just looked childish and less professional each time. But democrats just don’t have any presence until Obama and biden