This is not new here is SoCal. Back in 1976 traffic planners re-purposed a general use lane on the Santa Monica freeway to be a carpool lane. It was a public relations disaster and lasted just 21 weeks. It even spawned a parody song "Driving in the Lane with Diamonds" sung to "Lucy in the Sky" which got quite a bit of play on the old Dr. Demento radio show.
Driving In The Lane With Diamonds by Big Daddy
Since then all carpool lanes were built as new additional lanes with much less opposition.
The road diet implemented in LA got the mayor nicknamed "Gridlock Garcetti". Bottom line, proposals that involve taking away existing auto lanes are political losers. Having to drive in SoCal, I understand the feeling even though I ride bikes. Right, wrong or otherwise, IMO these road diets damage the cycling cause, making us the target of drivers' wrath.