If the bidding system is not disclosed, then it becomes trivially easy to cheat. With knowledge of your bidding system however, I can now determine that your bidding was indeed consistent with how you got to your final contract. (My system notes with one partner comprise over 30 pages of densely typed notes, and some expert partnerships have much more than that. It is not necessary to have such complete notes, but it can be useful, especially if some question comes up about one of our bids. On long drives to a tournament, my partner and I usually spend the time discussing these notes, often adding new points as we think of them. It all depends on your investment in the game.)
As an example, long ago, in a galaxy far, far away, I played a lot of pinochle. Partner and I developed a complete bidding system for pinochle, that was completely disclosed to our opponents. The only information passed was by the numeric jump of our bids, but we did reasonably well in passing what info we needed. Our frequent opponents were told of our system, and we explained the bids as we made them. Interestingly, after a while, our results suddenly went downhill, then we found out why. Our opponents had come up with their own secret system, that involved tugs on their ear, etc. We gave up the game completely, as there was no longer any reason to play, certainly against those opponents.
The point is, without disclosure, the game is a waste of time, no longer a game at all. At the very least, it is no longer bridge.
Next, bidding is indeed a major factor in bridge. If you think that just knowing what contract you are in is all you need to know in bridge, then you have a lot to learn. A huge part of bridge is correlating ALL of the available information at hand, bringing it all together and using that information to then play the hand. For example, did your opponents overcall? Did they bid at all? Even if they did not, it is still a case of the dog that did NOT bark in the night. Use all information to play the hand. Until you do that, you are still a novice.