because we don't want our engaging content to be made brain-dead easy.
If you don't party with me, I dont care how good you are in the game. But don't go demanding the content that everyone shares be made easier just for you.
edit: after reading your question again a few times, it sounds like you're imagining a single player game. Lets imagine Zelda BotW. OF COURSE, no one would care how someone else plays that game because it's a single player game and nothing they do can affect you in your game. But MMOs are a shared experience and FFxiv is based on teamwork and working together. Almost all of its content is based on teams. Naturally, if you're on a team, you should be concerned with your teammates' efforts.
