(1) I wasn't aware of it, but I am not surprised that something like this was written into the standard (presumably. I doubt carriers rolled their own thing)

(2) All the ways I can think off are significantly harder than rooting, so essentially no.

(3) I don't really mind that much, I have Google services running on my phone and I am certain those can do far more than my carrier could ever dream off. I have begrudgingly accepted those, so it would be a bit hypocritical to complain about my carrier turning cell broadcast back on. Especially since "turning cell broadcast back on" is a use case that I can see the argument behind.

It you care about this then I suggest you look up the relevant standard documents, probably you will find this behavior documented there.