[bbor]

“The model does not hold” === “existence wouldn’t be possible”. We found atomic particles, then did some more experiments and found quarks within the atomic particles. The quarks appear to be complex but predictable subsets of the particles. So “why do those subsets add to 1” invites a tautology, because the whole reason we found them in the first place is that they add up to exactly one, and therefor can be part of atoms.

It’s like asking why the left engine of an aircraft happens to emit the same amount of thrust as the right engine; if that wasn’t the case, there wouldn’t be a plane to talk about in the first place, just an art piece or a flaming crash.