"I have to disagree with."

Same. Sports and e-Sports are both easy to pick up on as far as objectives go. It's the various details and rules that take some time to pick up on, whether you're talking about NFL football or WoW arenas.

There are 22 football players on the field at any given time, and it takes some time to learn all those positions (similar to the classes of WoW). It also takes a little time to figure out what they all do (similar to a class' role).

Then you have different play calls, on offense and defense (similar to trinkets/positioning/cooldowns). And then there's the various rules/boundaries/penalties/etc (similar to having to wait to use a cooldown again, LoS mechanics, and so on).

So I would say both are pretty similar. The reason one is more popular than the other is because WoW appeals to a far smaller audience than the average joe watching the Cowboys at 1 pm on a Sunday afternoon. If it was all about the game being easy to understand, then soccer, tennis, and golf would be the three biggest sports in the US.