The obvious answer is that that's when the least number of players will be bothered, and indeed, that's what the wise and kind Nethaera says. But there's no way that time is always the lowest population every week, and sometimes maintenance, as it will today, runs long anyway. Why not Wednesday morning, or Sunday morning, or Thursday midafternoon, or Saturday evening? Actually, that last one would be a problem. But you're always going to inconvenience someone, so why not move it around a little and give those Tuesday players a break?
Neth says they're "always going to choose to do what needs done for the most benefit of the health of the game and servers." Which is fine by me-- back when I worked in retail shifts, I usually had Tuesday mornings off and couldn't play, but with my 9-5 now, it doesn't bother me anyway (and the recent changes to have restarts rather than downtime help, I'm sure). But are you someone who's been screwed out of gametime every Tuesday? And if you're not, would you mind giving up your playtime one week just so the folks on Tuesday morning wouldn't have to deal with the downtime and the restarts?