>I think there is some underlying personality trait that might cause both aspects.

Low intelligence?

I suspect this tendency is not correlated to political leaning in any way, and the suggestion that it is says more about how you want to perceive people of a particular leaning than anything about them.

There is a lot of research that personality traits on political leanings are correlated. So maybe that same common cause also affects humor?

https://pmc.ncbi.nlm.nih.gov/articles/PMC3809096/#:~:text=Th...