I think this is a good explanation, I think it has to do with the understandability of the game.
Like most of the people in the world knows soccer, basketball because the rules are easily understandable, the team with more points wins, and they win by scoring goals.
Chess, you win by eating the enemy's pieces until you manage to kill the king.
In contrast, MOBA, you attack towers, you kill heroes, you level up but ultimately the winning objective is actually you just have to destroy this building. Without knowing the complex rules of the game, you have no idea who is winning.
So long you have never touched MOBAs, which is a lot of people, you have no idea what is happening while watching a game.