People who want to play casually can do each piece of content one time.

People who want to play all of the time can get mounts that are put behind fun grinds that give them a reason to experience the content a lot. Every time they do the content it's different because they get a different party and meet different people.

A game company can't give them 365 days worth of content that doesn't involve repeating something. If they want that the only way is to play multiple games.