Because the US has some insane fascination with everyone being equal, no matter their own personal interests.
We hold these truths to be self-evident, that all men are created equal...
The US Declaration of Independence.
While it's patently only true subject to certain qualifications, it is still the guiding principle of the United States of America.
Nothing can be done about innate inequalities like musical talent or mathematical genius. Nor are one's acquired or inherited resources addressed. But it does assert that inherently, no person should be favored over another in how they are treated by the government or, indeed by society in general.
It was never 100% true. Equal treatment has been an ongoing progression since the nation's founding. And there are times when people can't really establish what qualifies for equal treatment, even allowing for the base political aspects where conservatives are inclined to shrug and say "that's just how it is" and liberals to apply a series of successively larger hammers to force equality where there simply might not be any.
Thus, debate takes place in many times and many places. But the reason for the debate dates back to the very founding of the nation.