In fact, that's exactly what they say they're doing: Picking windows where the fewest players are impacted.
And they've even shifted the window in cases where they know special circumstances will cause different population patterns. I can't remember exactly which day it was, but they shifted a maintenance into the early morning in the US because some holiday was going to mean that a lot of European players would be playing during the mid-day.
Sure, it sucks for the people who play at the less popular times (beyond the normal lower population issues), but it does seem a bit selfish to say that its better to inconvenience 10 people than 5 people because one of those five people is you.
Actually, most people aren't complaining about the time of day - they are complaining about the huge amount of unscheduled maintenance days that have been happening recently. We have no problem with *scheduled* maintenance happening in the middle of our prime time. It's all the other days recently we have been missing out on. If BioWare stuck to their schedule like most other MMOs do then no one would be complaining.