Networking Question

I’ve always been confused as to why the games networking is implemented the way it is.

I am not confused by the technical aspect of why things behave as they do, but more the philosophy behind the kind of iron-fisted validation & correction of most client input, be it movement or something completely aesthetic.

I am sure there are great reasons for the multiplayer aspect of the game to be built around this sort of model given the large amount of effort that goes into programming good prediction and the drawbacks that come with it, though I am not knowledgeable enough to know what they are.

So, why is it the way it is?