I agree you do not see as many bimmers here in Mexico as in the US let say Miami,or L.A, but you also do not se many bimmers in Laredo or Dallas
In Miami and L.A you see them everywhere. I studied in Miami or eight years and I know what I am talking about. Also you can see many many Porsches, Mercedes, Audis, Aston Martin, Maseratti etc as if they were given away.
One more point to consider is in the US most people leither lease or credit (credit rates from 1.99% special rate up to 6% or 8%, correct me if I am wrong) their cars and you can lease a luxury car for about 399 to 599 a month, and in Mexico, most people who buy a luxury car either by them cash or buy them credit (credit rates 14% to 16%, very expensive) in that case you end up paying from $800 to $1,000 depending on the downpayment and the years the credit is for.
Here in Mexico you have to go to the wealthy areas and surrounding otherwise you will not see them as often as you would want to. We have to consider that the level of insecurity, robberies, carjacking and kidnapping is around the corner, so that is why many people avoid having an expensive car and rather move themselves in affordable cars like Hondas, VW'w, Toyotas, Chevrolet and Dodge.
My 5 cents