You’re wrong. More Mexicans get in legally than any other country.
Nowhere near as many as we need if we had a realistic short-term visa program...but you may not be aware that Obama issued an administrative order in February, 2009 that made the raw numbers for each country the same. This was meant to increase Muslim immigration, since these very small remote African countries now had the same status as Mexico, a large country that is a neighbor.
Forget the law. He is doing everything through administrative orders, which is why he’s not very concerned about an immigration law and in fact probably doesn’t want a new one.