This is par for the course in MMO games. Things change over the years, expansions add more levels and abilities that need to be balanced, new classes, and so on. The shortening of the main quest has been asked for for a long time because of how much of a slog and how many pointless filler quests there are in the 2.X story. Considering you have to do the main story of every expansion, it makes it more difficult for new players to get into the game to play with their friends, for example, because they have to slog through some seriously boring stuff in that section of the main story.