IIRC, biennial sessions used to be extremely common.
Why would you think that? It's not true.
https://www.ncsl.org/research/fiscal-policy/state-experience...
> One reason for the change was the resurgence of state legislative power in the middle of the 20th century. Legislatures’ growing role in state government can be measured by the shift from biennial to annual legislative sessions. In 1940 only four state legislatures held annual sessions—and Alabama's legislature met only once every four years. In 2011, only four states still have biennial sessions—Montana, Nevada, North Dakota and Texas. Two changes came recently: Arkansas with its first annual session in 2009, and Oregon with its first in 2011.
In 1940, 34 states had populations of 1 million+ and only one state had a population of less than 100k: https://en.wikipedia.org/wiki/List_of_U.S._states_and_territ...
But the law is crazy, unconstitutional and would start a tit-for-tat form of legislating that would completely delegitimize whatever legitimacy the government has left.
Note, the legislature is weird. It meets every other year, is basically a second job. Not sure Cali's professionalization of politics is better, but something has to give.