The reason they are not standardized is that the federal government does not have control over the primary elections - and the states have no incentive to standardize them. They benefit from the exaggerated and brief attention generated by the primary frenzy within their borders. The increase in room tax revenues alone in New Hampshire is probably a huge boost to a place that would disappear from everyone’s attention span if we went to a national primary.
I understand, I mean "why" in the larger sense. The answer of course is that the earlier states like the money that flows into them--thus, the states that care more about getting a few more bucks for themselves are in the position of choosing the nominee for ALL of us. Wow, how's that for patriotism?