That is actually a great point. When was this law made?

Also, this only protects people who are aware of it and willing to fight for it

I do not know when the law was made. But the text of section 2872 at the bottom of that page suggests it was somewhere around 1980.

Interestingly, I met many people in SF who had signed contracts that disagree with this law.

I was alarmed to discover the same a few times -- the contract had wide claims on IP, and then there was a separate part which said "of course, these are the enforceable limits according to this particular California law."

It seemed like they were pulling a fast one, but basically they were compartmentalizing so they could claim the maximum rights should the law be struck down or repealed (or the business moved outside California, I guess).

That's OK, the law takes priority anyways.

Both Bay Area companies I've worked for include California 2870-2872 with their new employment packs, right behind the NDA.

That is required by 2872.

One anecdote for another. I'll take it.