I think drinking hours are a compromise from the time when alcohol was outright illegal. Also, many people who drink agree that its not healthy to be drinking between 2 and 8 in the morning anyway. A lot of foreign countries have similar rules, although a lot don't.
In many states, including my own, there are counties and cities that are 'dry' = meaning no alcohol is sold. Hard liquor can not be sold on Sunday in liquor stores: although it can in bars. Also, some other cities limit alcohol hours further than the state does, and some other places allow drinking in only private clubs.
I think the 2am rule has probably been good for me, although I love trips to New Orleans, Vegas, Amsterdam, etc... where the party never stops. There is nothing quite like sunrise on Bourbon Street.