One thing you need to understand is that the top "amateurs" are HARDLY amateurs. Dancing is their lives -- they train as much or more than the pros, and they also teach and coach and get paid for giving workshops and shows. "Amateurs" going to some of the top "amateur" competitions in Europe get PAID to be there -- their plane tickets, hotel, and entry fees are paid for by the organizers and sometimes they get a stipend or appearance fee for being there.
Really, the only difference between the elite level of amateurs and pros is which dance organization they are registered with. The "amateurs" dance in IDSF (International DanceSport Federation) events at the highest international level, and the pros dance in WD&DSC (World Dance and DanceSport Council) events. It's like with figure skating -- they got rid of the term "amateur" years ago, and even though it's not talked about on TV, those people you see in the top spots at the Grand Prix events win tens of thousands of dollars for placing that high.
Now, further down the line, when you start talking about people who dance purely as a hobby and don't spend all day every day working on their dance careers, then you will see a very large difference between them and the people at the top.