I suspect that this is being done the way it is specifically because it staggers interest. People who jump on it right away on Monday make up a large chunk of players. But they are a subset of the whole player base, while people who can only play consistently on weekends makes up another large concentration of players. If they reset on Friday, those two groups would converge, and you would have an unacceptable spike in usage of a single service in a short amount of time. I actually wish they would take it in the other direction, and stagger the resets a bit. Make Tomes reset on Monday, Crystal Tower reset on Tuesday, and Coil Reset on Wednesday. That would produce a much more beneficial distribution of resource usage for both the company and the community.

By staggering them, you also provide an artificial impression of priority. After Tomes reset, there's a grace period, then Crystal Tower has the "most" time, while Coil feels more compressed into the weekend. It's all artificial, of course, since each reset gives a full week, and you can do each activity whenever you want and still receive all of the rewards for it. But that impression of priorities would be a subtle tweek in the player's perspective towards the intent of the developers. Of course, you could mix up the resets to give the impression of other priorities.