Dota do require skill and quite a bit off it. Teamfights are down to timings and coordination, playing against other heroes is down to knowledge about them, pushing is down to coordination.
If you play late game protos your main army might have Vortex, storm and guardian shields as spells and you have to worry about splitting, position, keeping up production, maybe drop harassing and drop microing units. A tech switch from your opponent needs to be immediately answered and his harass squashed. It's really not comparable. SC 2 is notorious for being hard to play and that's also why its following is smaller.
MOBA games are more beginner friendly and thus have larger communities and viewer base.
I'm not bashing MOBA games, I think they are great, but even though there is definitely skill involved in playing them, that's not where they get their popularity from and it is not harder then SC2.
Saying that LoL games are more varied then SC2 games are also false. They might look a like on the surface but I dare you to find two SC2 games at the pro level where cheesing is not involved which are exactly the same.