mikopotato: but,,,, you cant play em all... :(
Breja: No, but I can play more if I don't waste time watching other people do it :)
Time spent on something entertaining isn't really wasted. Plus, you can do other things simultaneously while watching a video, such as cooking/ eating/ or working on something. With most games that's not really possible while playing them yourself. And then of course, there's exclusive games, which you may be interested in, but can't play since you don't own the required hardware.
TL;DR: There's valid reasons for watching a video of a game, instead of playing it yourself. And depending on the video host(s), it can be a really fun and/or informative experience.