Totally agree on the giant circle jerk that is California conservation politics (which IMO are all show and hot air, no realistic action - except when it comes to stopping any sort of actual necessary stewardship work like fuel reduction or development of higher density).

That said, the reason new dams haven’t been built is simple - all the areas worth damming already have been. There are only so many areas with enough dammable area and enough precipitation to make it even a little worthwhile, and those were all obvious by the 40’s and dammed up by the 70’s-80’s at the latest.

It isn’t even about how close something is - hetch-hetchy slaked the thirst of most of the Bay Area, and that is a solid 5+ hr drive away.