Matt, the California Energy Commission (CEC), appointed by the Governor, has been firmly under the thumb of natural gas interests for a long, long time.

It wasn't always that way. Back in the 1960s, even Sierra Club recognized the importance of nuclear energy for protecting the environment. President Will Siri:

“Nuclear power is one of the chief long-term hopes for conservation, perhaps next to population control in importance... Cheap energy in unlimited quantities is one of the chief factors allowing a large, rapidly growing population to set aside wildlands, open space and lands of high-scenic value. Even our capacity and leisure to enjoy this luxury is linked to the existence of cheap energy.”

Big money changed all that "conservation" nonsense:

"California’s former Governor, Edmund 'Pat' Brown, Gov. Jerry Brown’s father, started helping the Indonesian military dictatorship raise money to expand its state-owned oil industry. Pat Brown eventually raised an astonishing $13 billion ($100 billion in 2017 dollars) mostly from U.S. banks, the Sacramento Bee’s Dan Walters reported in 1990. In exchange for Brown’s services, the state Indonesian oil company Pertamina gave him exclusive and highly valuable rights to sell Indonesian oil in California...

At the very same time, another top Brown political aide-turned appointee, Richard Maullin, chairman of the California Energy Commission (CEC) began pressuring the state’s utilities to burn more oil rather than shift to nuclear energy.

And Gov. Brown appointed his friend and Getty Oil investment manager, Bill Newsom [present governor Gavin Newsom's father], to the State Superior Court."

Jerry Brown's Secret War on Clean Energy

Brown can take credit for being one of the chief architects of the modern anti-nuclear movement, and the fiction solar/wind/energy storage is anything but an excuse to sell more oil and gas.

Presumably the CEC, under the direction of Brown/Newsom, wanted to conceal the critical role natural gas played in keeping California's lights on until PG&E had committed to shutting down Diablo Canyon. That would make sense, anyway...but not much in California energy policy makes sense.

Above - Jerry Brown addresses a crowd of nearly 30,000 people at a "No Nukes" rally in San Luis Obispo, promising to oppose construction of Diablo Canyon Power Plant (1979).

Gary, new investment is unnecessary - it's only a profit center for utilities and an added expense for ratepayers.
There's no reason to shut down older assets, especially ones that already serve the public with dispatchable, carbon-free electricity.