I wonder if the lack of interest in content nowadays is in any way related to the general player disconnect with the story and the direction they've taken it in.

I feel like Dawntrail rendered a lot of the lore, world-building and atmosphere of the past arc completely meaningless, and there are no concrete rules or boundaries governing the story anymore. The consequent lack of identity makes the game feel soulless, and without that sense of investment the often tedious reality of MMO grinding becomes more difficult to justify. Yoshi P said something about the demands of the market changing and making the game require less time to play, but I think you find the time for something you actually care about.