For the same reason that in the airline no one starts flying on a 747, first you learn to fly regional on a 737/320 or for general aviation Lear/citation/rayteon and then you learn how to fly around the globe..
Which flying skills will you learn sitting in a cockpit for 12hrs talking on an HF radio when you would barely understand a Chinese talking in English on a VHF (for this also 10000hrs might not be enough)
Why does people always want to skip all the steps that the others have done!!????