Very interesting discussion.
I stumbled across a clue that additional hardware may be involved in lane centering. Go to the following Mazda Mexico link I stumbled across in a Reddit thread; Google offered me an English translation option:
Conoce más sobre la tecnología i-Activsense de Mazda, que te protege de los peligros en tu camino por medio de cámaras y sensores.
www.mazda.mx
Now click on "Lane Maintenance Monitoring System". It is then further identified as "LKA".
This sounds like a lane centering function that uses both sensors
and the forward camera. The radiating lines in the picture might be an indication the sensors are in the side of the vehicle.
Now back up and click on "Lane Change Monitoring System (LDW)". This seems to combine in one term what in the US we know to be Land-keep Assist (LAS) and Lane Departure Warning (LDWS). My US manual suggests these functions operate using the "Forward Sensing Camera" exclusively which seems to coincide with this Mexico LDW description.
If there are in fact side sensors in Mexican models, that's an odd choice of term since the vehicle would have to "see" the lines with a camera. This is watered down marketing literature; the side sensors may be more accurately described as "Side Sensing Cameras" if they in fact exist just as the forward camera is called a "Forward Sensing Camera" in US lingo.
If my conjecture is correct, Mazda may have added these side "sensor" cameras for Mexico because the Forward Sensing Camera's field of view is too narrow and/or down-the-road-looking for its other functions to be able to do the job of centering with enough precision at highway speeds to keep the vehicle from jogging back and forth from line to line. I've seen a reference to Mazda 3 having a lane centering function at speeds under 40 mph when the automatic cruise stop-and-go is engaged. That may not require the side "sensors" given the low speeds but I did not delve into that any further to know whether that is specific to some markets.
Here's what I don't understand. Doing a word search on "Mexico" in the PDF version of my 2020 US manual returns 70 references covering a variety of topics which leads me to believe it covers all of North America. But there are no Mexico references to these "sensors" or lane centering. Perhaps extra side sensors/cameras are a 2021 variation added for Mexico. I tried once to download a 2021 PDF manual from a third party and got a security warning and that brought me to the end of my curiosity on that question.
Even so, whether or not additional side sensors/cameras are required,. why not offer lane centering in the US and/or Canada?
@RubyNeal may be correct--a liability concern. I don't know how these semi-"autonomous" functions are marketed in other places but besides Musk's nonsense I've also seen a US Cadillac commercial with a woman taking her hands off the wheel, leaning back and smiling. Perhaps Mazda fears the US or US/Canada markets have been uniquely deluded. "Autonomous", semi- or otherwise, should be stricken from the automotive vocabulary for now and probably some time to come. Or it could simply be Mazda finds US law is more open to liability claims. I can't speak to that, but if so it sure has not deterred other automakers from adding this function and presenting it in overly optimistic ways.
I'm also in agreement with
@RubyNeal that even the LDW and LAS are kinda sketchy, though my experience is different. Even after coming to understand these functions only operate when very gradually sidling toward a line, in several of my tests reported elsewhere some months back along with normal driving since, I've found my vehicle picks up shoulder white lines quite consistently, rumble strips or not, but is very inconsistent in picking up left side yellow lines that are clear as a bell on perfectly clear days on two lane blacktops. I have not done enough expressway driving to judge how consistently it handles left side white lines. Perhaps my differing experience from Ruby's is the result of our forward sensing cameras being mis-calibrated in different ways. Who knows, and I digress, other than to say it begs the question of how well Mazda's the lane centering works wherever it is available.
As a final digression, I'm more interested to know if there is a software code modification to make the turn signal volume louder than the loudest user setting but alas I find no TSB for that.