I think a lot of this is that Republicans used to follow what used to be the recommendations of the most prominent main-stream economists. We can judge that as foolish in hindsight, but, “let the economics experts handle the economy” is a fairly reasonable policy.

2 big things changed. Republicans push more and more policies that economists consider dumb and economists have updated their models and recommendations based on new research. Even those old free market economists were not fans of tariffs and trade wars. It’s pretty hard to find an actual economist (like with a PhD from a respected econ school) who thinks wanton deregulation is a good idea.

At the same time, Democrats still hold on to a few ideas that economists all agree are dumb. There’s tons of evidence that things like rent control and home purchase credits make housing problems worse.

Democrats tend to support better economic policies than Republicans do but they support enough bad ones that it’s easy for Republicans to argue that the old status quo is correct.