Because people rich enough to buy coastal California real estate will be dead or in a nursing home by the time this happens. Or if they’re young, they have enough money that loosing a couple million is a cheap price to pay for living on the beach.

It looks like with California beaches you typically don't have to go as far back to find higher ground than you do with say Florida beaches. From the pictures I've seen a lot of the beachfront houses are built one stilts, often with the back at the level of that higher ground behind the beach.

I don't think they built this was anticipating climate change--it was so if a bad combination of tides and storms pushed water far enough up the beach to reach where the house is it would be under the house instead of in the house. Nevertheless, it looks like a lot of these beachfront houses could take a meter or two of sea level rise and still be above water.

They'd have a lot less beach, so it would probably change the kind of person who wants to live in them, but it is quite possible that they would remain very desirable.

As far as things not actually on the beach goes, playing with the interactive sea level rise map from NOAA linked in kibwen's comment, it looks like there are a few places (such as the Long Beach area) where you get some extensive loss of land a ways in, but for most places on the Pacific coast it is just the beach itself that gets lost. It is more of a mixed bag for places not on the coast but on rivers or bodies of water connect to the coast.

The same reason places like Miami have a red hot market and construction is booming. People either can't fathom sea levels rising to the point of catastrophe, or they think a 50-100 year timeline is long enough to not really be relevant.

Miami Beach is one of the more precarious positions worldwide and the real estate market there is barely reacting to it with high elevations now commanding a slight premium over prior years even in poor areas. It looks like we collectively are only going to react after the fact even if some of us are worried about it individually.

Most condominiums built today using concrete-rebar construction will be torn down in the same timeframe. Concrete rebar has a lifetime of about 100 years, even when properly maintained.

But nobody buying a condo today looks at what the resale value will be in 50 years.

For institutional investors it will react maybe one quarter before it actually happens, and for retail it could continue even with their feet in water with good marketing.

They are. It's just that after they sell the property, they already extracted all the wealth they needed.

Or, in other words, why would they react if their clients haven't?

It’s 50-100 years away.