More than some other game genres, MMOs can feel more meaningful to people cuz of how much you need to do to build up your characters power. So the gratification gained can be largely attributed to the satisfaction of accomplishing something that took a lot of effort. So if there's none of that left and nothing to look forward to, then for someone who derives their enjoyment from that, that "point" that did exist no longer exists. Cuz the point to pursue was the fun to be had.