The dynamic range of wealth and power is that one family can have 100,000 times or more wealth than another family. That dynamic range is compressed by a controlled environment like the SAT test: all the wealth in the world can't raise your score by more than 30% or so. If anything, a poor kid has a chance of showing what they are worth on a test like that whereas some rich kids can't test their way out of a paper bag unless they outright hire a ringer to take the test for them -- giving a badly needed form of downward social mobility.
Putting focus on the SAT helps to further obscure the real methods of "achievement laundering" by which rich kids can turn their family wealth into the illusion of accomplishment and leaves those unexamined... In the name of equity!