Well asked! I've been trying to understand why I do.
I think it comes to this: Good places to live come from encouraging and empowering people to make those places their own, as communities.
What it means to be a democrat or a republican changes from place and decade to decade. What is effective in actualizing that community participation then also changes as a place changes over time (ironically, that's also why it's important to have that community participation).
AFAIK, the Republican party _used_ to stand for small, decentralized government; now they stand for ineffective and centralized government (despite the talking points).
I'm less clear on what the Democrats "used to be" (except racist, way back in the day), except that in this era and in these places, community participation is hampered by unaffordable housing, unaffordable and/or inaccessible healthcare, and a lack of living wages.
I know I haven't fully answered your question, but I've been at this for far too long. Thanks for asking so effectively!
However, the fact that party vote in California changed in 90s, when it's been already a prosperous and desirable state remains. So it does not seem plausible that liberal policies turned it into one. The opposite though, is completely believable - in a rich locale, with a lot of money, politicians who use the money to "buy" votes will eventually rise and will remain in power until the money's gone.
Why would you think so? For example California used to be if not a Red State then a heavily leaning Republican: since 1880 until 2000 it has not voted for a Democratic president who has not also won the national election (and the 1880 election was extremely close). In the same time period it voted for a Republican candidate who lost the election multiple times (e.g. it voted against JFK and Carter).
Do you really believe that California had not been desirable before it started voting exclusively D (in 1992 the earliest)? I had not been living in the US at the time but judging by the popular culture it does not seem to be the case.