Because some people enjoy playing a game with fair and consistent rules, and find playing calvinball to be frustrating bullshit that is very often obviously biased towards certain kinds of actions, decisions, player builds, even just outright biased toward specific players.
And the rules allows interesting situations and fun to emerge.
sv_cheats 1 may be fun for one but not others.
Edit:
I don't have a problem with bending the rules and going whacko from time to time but it has to be declared in session zero so that everyone is on board.
If you put internal consistency above fun then what's the point?
Because some people enjoy playing a game with fair and consistent rules, and find playing calvinball to be frustrating bullshit that is very often obviously biased towards certain kinds of actions, decisions, player builds, even just outright biased toward specific players.
Just because it would be cool doesn't imply that it would be fun (for everyone involved)?
And just because it isn't consistent doesn't mean it isn't fun for everyone either.
The point of playing games is to have fun, the rest is secondary. This includes rules.
And the rules allows interesting situations and fun to emerge.
sv_cheats 1 may be fun for one but not others.
Edit:
I don't have a problem with bending the rules and going whacko from time to time but it has to be declared in session zero so that everyone is on board.