Why not? The rules say so? Change the rules.
Go ahead, but you'll eventually have to settle on rules of
some sort, and by their very nature
as rules they're going to make some things sub-optimal and/or simply not allowed. Plus, at some point you have to settle on rules that won't change, at least for the duration of a given session/adventure/campaign, etc. Unless you like role-playing Calvinball, I mean.
No, the entire point of having rules and restrictions is to avoid playground-style arguments of “I shot you!” and “No, you didn’t!” Hint the rules can be as light as you please and still serve this function.
Your first sentence strikes me as a restatement of my original point. Adjudication means some things have to be restricted, disallowed, or otherwise ruled out. Plus, you kind of need rules beyond task resolution, i.e. determining what characters are capable of in the first place.
Maybe for you. I think it’s a bug. The only limit is your imagination. So stretch your “legs” and see what’s out there.
There's a reason why so many RPGs don't simply ditch rules and say "use your imagination." Paradoxical as it may seem, limits encourage creativity.
For a concrete example. Planescape. I can think of no more freeing and wide-open setting that is utterly let down and failed by its restrictive rules set. Why play a human when you could play a slaad or a beholder or a dragon or a modron? Why be limited to what the book says you can do? It’s imaginative play. So play and be imaginative. Don’t just pick items from a pre-digested menu. You can do anything you can imagine. So go play.
The "play" part of it requires rules and boundaries in order to facilitate. By all means, go ahead and play as a great wyrm dragon while everyone else is playing as a low-level human. But even presuming you have the rules on hand to adjudicate what such a character can do (as a PC), see how much fun that is for everyone else; we've had how many threads here about the martial/caster disparity? Play as a dragon in a party of humans, and you'll see a much greater disparity.
Rules and restrictions are what turns "play" into an actual
game.