California is just very big and covers most of the west coast.
If you combined the top 2/3 of the entire east coast into one state you would likely have a rather anti-gun state as well.
The metro areas of Boston and New York City, Philadelphia and D.C., with the population dense region of Jersey, along with the generally anti states of MA, CT, NJ, MD would have a greater population of voters and representatives to overcome the rest of the states along the coast.
The gun laws of Pennsylvania, Virginia, New Hampshire, Maine, Vermont, etc would be much worse if it was all one state.
That is the situation in California.
In California the majority of the state by area is not anti-gun. The Los Angeles Metro area along with the Bay Area represented by San Francisco tend to dominate California politics and contain the majority of the population of voters however.
Those portions of the state speak heavily against firearms, highlight their misuse, and children and young adults grow up in a manner where they don't learn to expect or understand firearm freedoms. As a result they then support or act indifferently to yet more legislation.
The anti-gun movement that swept the nation in the 90s and resulted in a lot of national level legislation never died off or had the backlash in California that resulted in most of the nation.
As can be seen by the passage of numerous anti-gun laws in the 2000's, many signed by Republican Arnold Swarzenegger (most of the Democrat candidates in the heavily Democrat state are even worse.)
Pro-gun groups and individuals have succeeded in stopping many laws that did not pass, and winning some court cases requiring better clarification of anti-gun laws (like specifically banning an assault weapon by name, not just all guns arbitrarily considered similar upon local discretion.) But you don't see the actual pushing back and a turning of the tides that results in pro-gun legislation passing and an increase in freedoms like in much of the nation.
The best efforts and a lot of cash just slow the passage of yet more anti-gun laws, reduce the overall number that pass, and require those anti-gun laws that do pass to be clear in what they do.
California would certainly be a lot worse already without these efforts, but it isn't getting better yet.