My guess is that it's the same reason games typically come out on a Tuesday in the US: sales tracking. Since sales numbers are so important (particularly in the first few weeks, when the bulk of the sales happen), they want to maximize the data by releasing on the first day of the data week. In the US, that's a Tuesday. I'm betting it's Friday overseas.
If a franchise is a juggernaut that doesn't need to justify it's numbers (think "Call of Duty"), they can release any day they want. They don't care if the first week's data is chopped in half.