I don't think the grind is really the issue here. I think that it is the reward. Not counting any kind of roulette bonus is takes 12 full runs of a dungeon to max out poetics for the week. Once you have done that what reason does one have to run the dungeon again for the rest of the week?

Now I am not saying that SE should start throwing mounts, and huge sums of gil at players to keep them doing things like dungeons, ST, and coil, etc, however generally the goal is to keep as many people paying to play the game as possible. If players are getting burned out or bored with the number of things to keep them busy from one day or week to the next then it becomes time for the developers to add or create something new that will keep player's interest.

The goal is to make the player want to log in on a daily basis to play the game. They do need something for players to make their characters better beyond just getting the best available gear for them.