it isn't just california. people are like this everywhere. not everyone of course is though. as seen here f'rinstance. there are a number of good anglers that practice catch and release. even of large fish. even californians. l release most bass l catch, especially the larger ones.
you must take in to consideration too that many fish are not large to begin with. most stocked trout in cali are less than 12". most of these taken ARE eaten. the majority of bluegill everywhere are not that large but are taken home anyway and eaten because they are so tasty. grunion are skinny things 6" long. hardly a mouthful. most taken are eaten.
if YOU really do care about this, you can make a good start by teaching your kids and friends about size limits and bag limits which again, l believe most of the people HERE (as you say) do follow religiously.