That makes some sense. When you're smuggling something you want it as pure as possible, so it takes up less space and is harder to detect. You cut it with something else after you smuggle it.
The same thing happened during prohibition. They smuggled hard liquor, not beer.
So… why the meth is coming aaaaaall the from Mexico? Wouldn’t be easy to get some of that inordinate amount of meth that is coming from the nasty country north of the border? Much closer… ;)