The primary one that no longer exists is the terrible lack of communications between various parts of the country during the days of the founders. Info today spreads at the speed of light.

The old argument about giving the small states more power might have been legitimate back when the largest number of electors a state would have might be 5 or 10 but today, when huge states have 40 or 50 votes, a small state with 3 or 4 is still completely outclassed by the population centers. Let's face it. The populous states are still the most important and always will be. If, as a citizen, that concerns you, then move to California.

Which brings up the 3rd point. We are this incredibly mobile society. Very few people today have this strong allegiance to a single state like they did in pioneer days. Often, people especially the elderly, have residences in multiple states, a summer home in Wisconsin and a winter home in Arizona. They can pick and choose which state they wish to vote in (and actually can vote in both if they don't get caught). Why add an extra layer of complexity to an already strange situation like that?

The idea of strong states rights is a concept that made great sense in history when each state was this little country in itself with major distinctions between cultures, industry and values. Today those lines are blurred greatly by the rapid flow of commerce and information.

Many functions of government make sense to carry out on as local a level as possible to prevent the bloat of huge structures from making them impotent. Somehow I don't think a simple act of a Presidential election falls under that category.