Originally Posted by
unbound
The only argument that really matters. It gives the illusion of more content while costing Blizz substantially less to maintain.
This is the same argument for Normal/Heroic/Mythic/Mythic+ dungeons.
Most dungeons, and pretty much all raids, can be done much faster than in the past (indeed, Mythic+ is based upon that concept). They no longer have to worry about creating a challenging, growing experience over the course of dungeons and raids, you create fewer and smaller areas with a difficulty slider.
I do think this is the reason that you have a big influx of players with expansions and patches, with a subsequent dive in subs as many people realize they are doing the same thing they just completed with a mild increase in difficulty to get the exact same gear they already have with slightly better stats. In any large industry, this is called a self-inflicted wound.