This is simply not true, it is choice he has made. While he may have good or at least strategic reasons for not speaking, there is nothing preventing him from saying, for example "I was taking X because _____ and this is what cause the test results". The best thing he can do is come out, admit to everything and be completely honest. The situation will die a lot faster if he tells the whole truth. Sure, he COULD say something, but as you've pointed out, he would be incredibly dumb to do so. Why give the MLB attorneys that much more time to prepare for his defense? Asking him to come out and tell his story now is just not a realistic thing.