This concept of a level playing field is a metaphorical representation of fairness.
Everyone wants to believe that when trading or playing or learning they have just as much of a chance as the next guy. There are times when one person does have an unfair advantage. Money, popularity and nepotism can give someone an advantage over another person in certain situations.
There are sometimes precautions put into place to try and help those who have things that tip things unfairly against them. This is why games have impartial referees or judges. A student who doesn't have money to go to school may get financial help for their education. There are laws against monopolies that control the market destroying competitors.