To us as gamers, watching a game is easy to follow because you know from experience what would be going on in any given match.
However, if you were to show a game of Hearthstone to someone like your parents, they’d have as much knowledge about the game as a child would about running a business. On the other hand, games such as FIFA, CS:GO and Rocket League can be very easy to follow.
If you were to show gameplay of the latter, anyone would be able to understand what the game is about - who’s winning/losing, and the fact the opposite team need to score an amount of goals to win.
However, games like DOTA 2, League of Legends and Starcraft 2 all have issues such as confusing gameplay and tactics, to multiple champions each having loads of spells and buffs.
Keeping track of this, alongside any other minor details is very hard and confusing to a non-gamer, and can turn anyone them away from ever watching these games again in the future.