I wouldn’t be unaffected if everyone had more max level characters. Part of my game is to level loads of alts and work towards synergy between my tradeskills. This allows me to make gold and items more efficiently which is a huge part of my game. If everyone can easily max out then this directly impacts my game.
Would you be OK if all current-tier endgame heroic and raid gear was added to be occasionally world drops or random quest rewards if raiders could turn it off? By your own logic, you could keep doing what you enjoy at max level while those who prefer just to level alts could have the fun of receiving all that loot without the unhealthy, boring option of raiding and running the same heroics over and over. If any part of you wants to respond with “No, you should make the effort for those items”, then you have your answer to my position on levelling.