As someone with personal experience at that level of sports, I can say that those athletes are not really amateurs, but they are not wealthy and are not all children of the wealthy and priveleged.
In many sports, competing at the international level requires so much time that holding a full time job is difficult, and the costs of traveling to qualifying competitions and international competitions is very high particularly if personal equipment is involved. The equipment itself can be very expensive and require special handling. Even a dedicated runner has his own "special" equipment, multiple pairs of shoes that are broken in just right, tape, powders, lotions, running clothes, water bottles, elctrolytes, it can fill a duffle bag, and if it gets lost in transit, its a disaster to that runner.
Competing in an international event may require several weeks, you have to travel there in advance, spend some time training and becoming familar with the climate, people, arena, equipment.
I don't think anyone competes at that level without financial assistance, but those athletes give up a lot to do it. Their sport is their entire life, it's more than their career, every waking moment is spent working or thinking about their sport. In that sense, they are not amateurs. But they are extremely talented, the best of the best, people blessed with natural ability and the dedication to refine that ability to its peak. If you think anyone can reach that level if they only had the time and money, you are very wrong.
