The reason why the option still appears is the fact that if the option was hidden, and someone saved their preferences, the way alert opt-outs are designed would mean that they would automatically opt out, even if that wasn't their intention.
Then, if you turned the option back on, everyone who saved their preferences before would remain opted out of those alerts, without any indication as to why.
In short: Displaying alert opt-out options for things you have disabled is (currently) required.