The reasons I was given for first Tuesday in November are:

1. After “pay day” at beginning of month (not everyone gets paid on the first of the month though).
2. So you will be sobered up from your weekend drunk.

The idea behind #1 is that it should be harder to bribe you if you have recently been paid. The reason behind #2 is that you will be sober when you vote.

Also, in my state at least, alcohol sales are prohibited while the polls are open for voting.