The question is essentially: Why are viewers satisfied with simulacrum of gaming(or similar activity)?
1.They get to watch skilled experts or people with experience.
Like sports fans cheering for their favorite sports star.

2.There is no chance of failure, loss or flustration. Streaming is a much more neutral experience vs gaming itself.

3.It doesn't require new hardware, game purchases/install/setup. Streaming is much cheaper and easier overall.

4.It doesn't require learning the game, builds and tricks that are needed for expert gameplay. There is no skill ceiling or mandatory learning - though you can learn from streamers you don't have to.

5.Like with watching people in film eating, there is co-empathethic experience of being "present" in the game without any effort or danger present.

6.Playing games takes time and dedication,but watching them can be done anytime and without interrupting anything else.
Streaming is essentially a micro-TV channel for the niche audience of game fans.