Things happen in trials and raids. The bosses don't simply stand there completely stationary as the players acknowledge what they look like and then kill them. The boss and players engage in combat, during which the boss uses various attacks and mechanics which are challenges for the players to overcome. Sometimes they have multiple phases, cutscenes and arena changes which are designed to be visual spectacles for the players to enjoy as they progress through the story. There is more to these gameplay activities than seeing what the boss looks like at the end of the fight.
The opposition to this change is bizarre. Does occasionally taking a few minutes longer to clear a main scenario duty while levelling an alt character bother you guys that much?