But, why....?
Anyone can play a video game. You can play it yourself instead of watching.
I don't get it
Take League of Legends. I both play it (ranked, low though, I'm old with no time) but marvel at some of the engages and whatnot teams can pull off and execute in a complete storm of activity.
Same reason I watch baseball. The matchups, the pitching, strategy, etc. There was a great match in League the other day wherein one team had a strong early game composition and the other team a late game composition.
The early team needs to close out early and they dominated everything early. Then it started to shift as the early game team couldn't close it out. The late game team started to win all the battles, so they (early team) sent one player sneaking through the forest (it's dark) and by luck happened to miss all the vision wards (which would have made the backdoor noticed) and won the game. Was exciting.
Plus, some of the streamers are really amazing and funny (like Nightblue3). He always stays so positive regardless of how things are going.
Once you get a good grasp of the game, it's pretty bonkers what the pros can do. Thresh is one of the best designed champions and a great Thresh outplay is fantastic.