End game loot is capped because the developers removed the time sink that existed in previous games that blocked players from getting endgame loot. I've played lots of MMOs where endgame loot was a matter of spending the time to farm lesser bosses to then spawn the bigger boss with the better loot. However, it would take dozens of hours to "prep" that. And these were all world-spawns - so you had to compete against dozens of other guilds/FCs to get the drop. You couldn't raid on your schedule. You had to raid on the schedule of when these enemies were going to spawn. And there was actual experience loss for when you inevitably died. And there was ridiculous travel time to get these areas.

FFXIV removed all of that.

Show up when you want to raid. No competition. No gil/experience loss. Enemies drop tokens that can be turned in for whatever loot you want... plus the bosses no longer drop trash. No more "oh look, yet another boots of maiming with skill speed for the no DRG/RPR in our group. You get a coffer, you open it and get the piece for whatever job you want. More loot for less time. This is the truth. And this is why it is locked behind a weekly schedule.