Many years ago, I was chatting with a friend from California and she told me her family votes Republican. As in, by default. No matter the policies or political needs of the country.
Aside from the US parties being very similar back then (pre-Trump), I’ve also learned since then that this may have to do with party affiliation programs.
In the US, you need to register to vote and the parties basically offer to do the registration for you, if you promise to vote for them. So, you end up being ‘affiliated’ with them, even without being actively a member.