I actually think we already knew this sort of thing has been happening for a long time:

Johns Hopkins University’s Institute for Education Policy released a study comparing older versions of the SAT with a current practice test. Although a change in difficulty cannot be established, researchers found substantial differences in the reading section that, across the examined dimensions, “point to the test becoming less demanding.”

Questions now loom over whether expectations for college preparedness have declined, and whether the changes signal a deeper problem affecting the school system.

Questions looming? Is there really any doubt it’s been happening?

More:

The changes include significantly shorter passages, an 83 percent drop in vocabulary questions that require independent word knowledge, the near-total replacement of argumentative and persuasive texts with expository ones, and readings whose meaning can be grasped through context rather than assumed prior knowledge. …

David Steiner, executive director of Johns Hopkins Institute for Education Policy … posited that the changes could be attempts to increase equity. “We know that children of more privileged backgrounds bring more background knowledge to a test on average, so by dialing back the amount of background knowledge required, you’re enabling a more level playing field,” he said.

Can’t have people who know more doing better, if it violates the DEI goals of education.

Also, background knowledge is hardly irrelevant. It grounds a person learning new information and allows that person to relate the new to the old, giving it context and depth. Background knowledge also helps a person evaluate the truth of what he or she is reading. I wrote a post on that subject back in 2016, and one of its points was that it is partly the schools that have failed to teach students background knowledge:

In other words, [book author] Hirsch says that kids from richer and poorer families start out roughly equal in skills, but since schools fail to demand that children learn facts that would help them understand what on earth they’re reading, the poor kids quickly fall behind because they don’t get that background information from their environment. This may sound like some sort of excuse, but it’s not; as I said, he mounts some fairly persuasive evidence that it’s at least a large part of the story (or that it was by the 1980s, when the book was written).

When kids are learning to read from texts such as “Dick and Jane played with Sally” (yes, I know they don’t use Dick and Jane any more, but you know what I mean) there’s not much context they need to understand that isn’t well within their easy reach. When they’re in junior high and high school, and they are reading a passage about the Civil War, Grant, and Lee (for example), it helps to know there was a Civil War, when it happened, what the issues were, and who the major players might have been. These need to be firmly in place before the children can understand what they read. And the lack of specific knowledge is cumulative, because the children who lack it fall further and further behind because they don’t want to read things they don’t understand, and more and more things become things they don’t understand.

It’s only gotten worse since then, and I see little to nothing happening to arrest the slide. One of the reasons is that teachers who are also culturally illiterate have come up through the system, and people who plan curricula are for the most part interested in leftist indoctrination rather than giving children knowledge and skills.