Earlier quoted context omitted.
Making test prep materials more accessible doesn't really sound like affirmative action to me. It's not an attempt to counterbalance this particular socioeconomic bias, but rather to remove it.
The socioeconomic correlation isn't a bias - it reflects the reality that a poor childhood leaves you less prepared to do well in college. Erasing that effect without fully erasing the causes of the effect is a cover-up that defeats the purpose of the SAT. Making the test harder to hack by acquiring shallow knowledge (like memorizing "SAT words" without actually being well-read enough to have seen or used them before…
What you are advocating amounts to intentional "handicap" for those who find test-prep tools expensive. Yes, you are getting higher distribution of scores. If you would single out brown eyed people and denied them access to those tools while giving them everybody else, you would get high scores distribution too.
Both tests would be just about the same useful. If the childhood leaves some less prepared to do well in college, then you do not need to add another handicap to them. They are more likely to fail even with access to those tools. If the access makes them perform better, then your "it is fair cause they are not prepared" goes out of window.
Note: I'm not saying they should not sell test prep. It is business and it is ok business to try to earn money. Just that the more expensive materials are, the less you choose on actual aptitude.