the educational systems are different. The US doesn't even have the MBChB degree, and I don't think that 'MD' means exactly the same in US vs UK or India or Aust.
For example, I know that a dentist in India first receives a BDS, then if they specialize they can get a MD. In this context, MD doesn't mean the same as the US 'Medical Doctor' MD. But their scope of practice would be similiar to an equivalent specialist in the US with DDS and MS degree (or Certificate).