I disagree. Case in point, there were no rewards for running Torghast in Shadowlands beta, and yet still we did it for dozens of hours nonstop.
Because it was FUN.
I get no rewards from drinking beer and playing soccer with my friends in the park. But it´s fun.
People play games for FUN. If they don´t, then the game is 
and as soon as the rewards go away nobody will play it anymore, there we agree.
BTW That´s one of the main reasons I don´t personally believe that anybody actually runs m+ for fun… because everybody that supposedly does so is complaining about the rewards 24 /7, be it here ir elsewhere. And people don´t usually complain about things they actually consider fun…
I mean, how many people do you know that say “Oh no, not sex again?” on a regular basis? 