Just a theory, but I think the absense of Mexico maps are most probably based on demand
The last 35 years i've traveled thru most of the states that make up Mexico.
Outside of major cities, the roads/highways are rarely congested. I've driven the entire distance down Mex180 from Texas to Veracruz to Cozumel. From El Paso, i've driven the Mex45-49 route all the way to Cetro, Mexico City. The majority of times my wife and I fly into Mexico City and drive from there. Wev'e driven form shore to shore and up and down both coast. Couple of times we've gone all the way into Guatemala & Belize.
Personal observation: As I mentioned, seldom have any roads i've ever traveled, would be judged "heavy traffic". The turnpike from Mexico City to the west coast is the only long stretch I remember ever seeing that had lotsa cars for a long distance. For one, I don't think Mexicans do "road trips" like we do here. Secondly, the roads are not the high speed type wer'e accustomed to. Thirdly, most family units live in fairly close proximity to each other. Therefore, cutting down on traffic. You see very few RV's, Campers,etc in Mexico. You see very few cars with luggage racks on top....
You do see allot of nice looking commercial bus lines. Not anything like the junk Greyhound buses of America. On most highways , you'll see a fairly consistant stream of ADO & UNO bus lines. I figure that's how allot of Mexicans travel.
I just don't think the Mexican population does anywhere near the kind of traveling we come to expect as natural here in the States. Their interstate highway system is not all that great and the road surface can be hazardous
for long stretches.
Anyhow, I just can't imagine Mexicans buying allot of Nav Gadgets