I think that people in the public eye, especially those that court controversy and make an effort to have an attnetion seeking kind of presence can expect people to ask questions about their private lives too. They make it easier on themselves if they give the information rather than let rumours and speculation flow.
I cannot think why he would not want people to know he was ill anyway, it is what it is, trying to hide it will not make it go away. He is a proud man and perhaps he does not want any sympathy. Who knows?
There has been a lot of chit chat in racing circles about what is wrong. Even scandalous rumours circulating which may, or may not be true. Apparently he goes to the US for some kind of treatment. He has had the shakes for some years now, but it has become more pronounced of late.
In person, he seems more fragile than on tv, could be age related, but he is not that old.