What is the point in disclosure of the bidding system to opponents?
Bridge players hate guessing.

Allowing non-disclosure will basically turn the game into a pointless guessing game, with luck (and to some extent, the bidding system) becoming the predominant factor, rather than skill. This will surely drive away the good players, and all that will be left will be self proclaimed bidding theorists...

Just because you cannot achieve 100% full disclosure does not mean you get rid of it completely.

The current rules [of full disclosure, different systems] allows for (somewhat reasonable) innovation in bidding while trying to pit opponents on an even ground, making skill the predominant factor. Making skill the main factor, with the right amounts of luck, is what keeps people coming back.