It is a simple matter of contract law - it is an exchanged for bargain. In consideration of you getting access to the SDK, etc., you are agreeing to a non discl

It is a simple matter of contract law - it is an exchanged for bargain. In consideration of you getting access to the SDK, etc., you are agreeing to a non disclosure clause and paying $99, among other things. If you don't want to enter into that agreement, don't. Shrink wrap licenses and related items are generally enforceable.