The real question then is why the "professionals" in these fields are able to command such massive incomes, and why people are prepared to pay multiple hundreds to watch their favourite singer but won't drop into a free gig at an open mic night. Why some footballers can can earn millions per week, and the lower tiers of the sport are paid so little. Why top actors can earn more from one film than even most doctors or lawyers will earn in their lifetime, while other decent actors spend their entire careers working as an extra, etc...
Clearly everyone can see that the system is "unfair" in almost every industry, so the question is why does everybody perpetuate this system. It seems to be that by and large, people are prepared to pay more to get more of whatever they consider "the best" and they care much less about everything else in that space.
But shift the focus away from people and to products - why are so many people willing to pay over $1000 for the latest iPhone, when they already have the previous year's phone, and a $100 phone probably does 90% of what they need.
Again, it's because people want the best they can afford, and so the market increases the price to the point that maximises the product of price and people prepared to pay that price. Sadly, for the aspiring musician that hasn't been scouted yet, the price is low and even then not many people are prepared to pay it. This is why we have record labels who scout for talent, front them some money up front, handle publicity and building an audience, hoping that one of their 100+ artists might make enough that they can pay for the rest and still make a profit.