At least with something like this, it would be relatively simple for the manufacturers to just enable the functionality based on where the car is sold.
Can't do anything like that with emissions regulations.
You totally can. VW's emissions cheating scandal was about the ECU firmware tuning the engine for lower emissions when it detected an emissions test and then switching back to tuning for performance the rest of the time. No reason you couldn't do the same but based on location.
I can see them attempting that, but it'll give legislatures in other states an incentive to make it law as well, simply from the view of "look they're treating us different" which usually pissed people off more than when everyone is treated shitty but equally.
Can't do anything like that with emissions regulations.