I think a lot of it shook out of the hippie movement, where some people were just self serving narcissists that wanted to do drugs, have sex, and didn't want fight in a war. Then when they got families and jobs they didn't want government "stealing" their money to help other people, and so they "became" conservatives.

So they just assume narcissistic motivation applies to everyone.

The sad thing is, in the US at least, we really need the conservatives to do actual conservative things. There is a definite benefit to looking at government action with a critical viewpoint, and saying "Should we be paying for this? Should it cost this much? Should we even be allowed to do this?" Unfortunately, they've abandoned that important role in favor of deepthroating corporations, peddling FSB propaganda, and forcing their version of the bible on everyone.

As others have pointed out, the likely cause is that politics doesn't change with age, it changes with one's investment in the status quo. The most likely reason that this effect is breaking down is because most people born after Reagan's presidency were never given any means to become invested in this system. If you've got no assets and lots of debt, fearmongering that immigrants are coming to take your job or wealth doesn't work.