Meth is a gigantic problem in the US and other parts of the world. According to the RAND Corporation, it's costing the US anywhere between $16-48bn annually (and these are 2009 figures, the numbers have likely increased since).
One simple solution would be to simply put pseudoephedrine behind the counter, which would procurement of the crucial precursor ("smurfing" - fantastic euphemism) much harder. Why don't states ban it? The answer is, as in many, many other public policy debacles, money in politics.