Because, through science, we are constantly improving our understanding of the world, including our bodies. Sometimes, that means things we used to think were safe or acceptable no longer are. We used to shit in buckets and throw it out the window in the morning right next to where the butcher was carving up a carcass on the street. We used to have parties when a kid got sick, so all the kids in the neighborhood got sick at the same time. Recently, we learned more about the impact of the compounds released and their concentrations when we burn natural gas in a confined area.

My understanding is that, while we knew about the compounds released by gas stoves, we either didn't know how high the concentrations were or didn't know enough about the dangers those concentrations could present. Of course, the reactionaries blow it out of proportion and a statement like "Gas stoves might not be safe without adequate ventilation" becomes "THEY'RE GONNA TAKE YOUR STOVE BY FORCE" just like how "cattle produce a lot more greenhouse gases than we thought" became "THEY'RE MAKING BURGERS ILLEGAL!"

Going by what I've heard, it's a growing movement to switch to green energy and the concern that burning any fossil fuels is damaging to the environment.

A lot of these articles, while using completely valid science, are also worded in such a way to help convince people of the health concerns (no matter how small) to make the change, which also helps the movement. Sort of the "any little bit helps," sort of thing.

Because electricity in California is deregulated.