It's not that simple. Plenty of liberals in California would stay home as well in past years because "the outcome is inevitable." But they'll be inclined to vote more this year for the same reason as Republicans.
The idea of California flipping is completely ridiculous by the way. Has about the same chance of happening as West Virginia choosing Biden. See how ridiculous it is to say "what if, even just 15% of those missing liberals in West Virginia came out and flipped the state"?
Extremely wealthy people. No different from a $20,000 bet on a hand of blackjack or horse races. It's just play money to them (and/or a gambling addiction).