Mexicans tend to spend their money on things other than an RV, they enjoy being waited on and pampered. But then again, so do some RVers. Ok, let's say they tend to invest money that has real value where as RVing as a life style there is little (or no) appreciation in the investment. It is a life style that in Mexico still screams "too poor to stay at a hotel".
It is no different that the USA or Canada, people do it, when it is within the range of their finances, because they like the idea. It is a niche class up North and will be the same forever here in Mexico.