Euclid wanted to show that all of these moves are always true and can be used in any conceivable combination or situation. He wanted to have a foundation so that if someone doubted that he had really bisected an angle, he could prove that he had. But the proof is really no more than the instruction how to do a certain geometrical move. When I ask for a proof, I want to know that you did it right. And a proof requires foundation.
Every demonstration requires a foundation.
Math needs a foundation so that you can use the foundation as the basis of your demonstration, so that you can prove to me that you calculated correctly. For if the proposition is a rule, a paradigm, which every calculation has to follow, then it makes no more sense to talk of working out the equation, than to talk of working out a definition. Wittgenstein here wants to say that we cannot prove the rules of our game. The axioms, formation rules, etc., are never proved within the game. A move like bisection is proved and provable.