Honestly, that describes almost every hobby people have where you do not use personal job skills by extension. (Sports, Reading Fiction, Social Planning...) MMOs are social platforms people play them more to communicate, but the platform is filled with lots of short term activities with long term rewards. That is to say the platforms are designed with carrots on sticks but you don't realize for a long time when your playing. Initially you wan to learn the lore, maybe gain skill at the platform and play with friends, but your friends are leveling up so playing with them is a moving target. Once your max level then you have gear score to keep up with to keep running new content. When you add collecting achievement systems and various other built in bottle necks you slowly realize your chizzling away at a very thick wall trying to tunnel out.
I personally can not believe blizzard did this. Wow isn't free to play thats 14.99 x 100k or 1.4 Million a month that is a lot of beer for developers. Something had to happen to really make them believe they had both good detection system that wouldn't have to many type I errors and additionally, removing the income would some how stem the tide of its legitimate subscription loss. I'm honestly surprised they didn't try to instead tax the accounts in some way via both in game and real world currencies.