Moar this than I can upvote. Getting in early changes your entire day. Sure, you sleep less, but unless you have an acute medical condition you can get used to it within a week or so.
I wondered the same thing. My reasoning is it forces you to keep your categories simple, which makes looking at the cards on the board easier.
If using lots of labels became the way things were done in Trello, it wouldn't have been so simple. The best thing about Trello in my eyes is your ability to refer it as a tool to colleagues. Many many times they would come back thanking me because Trello was what they were looking for.