This is actually a commonly misstated cause-effect summary of what actually happened.
First, the SAT or some variation thereof has been administered for decades. In the early days, it was predominantly taken by people with serious plans to enter college.
Accelerating from the 1980s onward, the SAT began to be used for a variety of purposes and was taken by an increasingly large percentage of the student body, and across a wider base of years.
For instance, the Duke Talent Identification Program routinely had SEVENTH GRADERS take the SAT. I myself took the SAT for the first time in seventh grade, and was selected for T.I.P. Now, I'll be the first person to tell you that my 11th/12th grade SAT scores were significantly higher than my 7th grade SAT scores. But as a 7th grader, my "lower" scores were a part of the statistical bell curve.
From the 1980s onward, almost every high school student was pressured to take the SAT. Including athletes. Including students who were likely to go to 2-year community colleges.
As a result, by the early 1990s, the MEAN score of the SAT had declined a bit. So the scaled score was RE-curved. Which resulted in an uptick in the "fat" part of the bell curve where most of the scaled scores reside. It was absolutely NOT some sort of "add 100 points to your score no matter what your score was" situation.
And this has nothing to do with the test being "slightly easier". In fact, the argument can be made that the format of the test is more difficult today. For instance, in the 1980s, you had exactly two kinds of Math questions. There was the traditional "5 answer multiple choice" question, and the the old 4 answer "comparison" questions (they gave you two columns of math information, you answered A if column A was always larger, B if column B was always larger, C if the two columns were equal, and D if it "could not be determined"). Since the 1980s, the test has added a mix of other formats, and you currently have a batch of questions that are based on interpreting charts or tables.
Similarly, the SAT Verbal was made up of Reading Comprehension, Analogies, Sentence Completion, and Analogies. The "Test of Standard Written English" was where you had your Grammar questions, but this section "(scored from a 0 to 60+) did not "count" as a part of your scaled score. Now, things like Analogies and Antonyms have been removed and the grammar components have been moved to the "regular" Verbal section.
I'm not sure that either math or verbal are "easier" than they used to be. And I think my nephews and nieces and family friends whom I have prepped for the SAT for the last 20 years would agree.
Can you prep? Sure. I've never seen any other test where people try to convince you "oh, you can't prepare, you should just go in there and do your best, nobody cares if your score is low". But that's what HS teachers and advisors try to tell HS students today.
Is it easier to afford prep courses and/or materials if you have more money? Sure, but that fact has never changed.
www.nea.org
cepr.harvard.edu