It turns out that there are thousands of problems various legislatures can choose to address. That they're addressing just a subset of the entire problem space

It turns out that there are thousands of problems various legislatures can choose to address. That they're addressing just a subset of the entire problem space with any given piece of legislation is a feature, not a bug. In this case, the federal tax treatment of inherited property (problem 1) cannot be addressed by a California state-level legislature, but the latter can try to increase the supply of housing in CA (problem 2) by making ADU sales legal there.