Because California stands for many, many, many, many of the things they oppose without evidence to back up their claims: Supporting LGBTQ+, better Social programs, limited religious freedoms, run by a bunch of "liberals", etc. etc.

And yet, it's the 5th largest economy in the world, and the vast, overwhelming, majority of funds for the USA.

They hate that California works, because it disproves pretty much all of their talking points.