Stupid
Yes - well here is the stupid part - people have been supposing and speculating and assuming and one thing or another since way back when they required ULSD in the US. At that time the speculators on this forum said it would be available in Mexico in 2010. Guess not. From then until now it has been a continual topic and it is not going to stop any time soon.
There is nothing simple about this. If you think there is a simple answer you haven't been paying much attention to how things work in Mexico. As Wanderer says - no one will know when or where there is ULSD in Mexico until it is available almost universally. Odds are pretty certain there will not be a station here and a station there. And they will not have it at Gulf and not at Pemex. Of course that is just more speculation. Let's see how the facts shape up when and if they ever do.