Schools cannot force students to learn. A lot of people are having kids because of social/societal expectations, lack of sex education, or lack of access to birth control rather than because they actually want to. As a result they are much less involved in their childrens' lives and expect schools to take care of raising their children for them. Stagnating wages and rising cost of living from inflation or corporate greed or whatever you want to call it means that even parents who do care are often too busy trying to make ends meet to be active parents. I suspect all of the above factors also correlate to parents who are not very well educated themselves.

If kids do badly, rather than encouraging or incentivizing them to do well or addressing their behavioral issues, these parents will instead blame the teachers. It is getting to the point where this is the case for the majority of students in many places. I have friends who teach in selective private schools, which would in theory correlate to more resources for students and more involved parents, but even there they are starting to see this.

Schools don't have the resources to address this crisis properly; schools are funded by tax dollars so teacher pay and overall school funding have stagnated along with wages. Schools cannot fail every student or hold them back a grade, and they are also incentivized to have high average grades, so they end up lowering their standards and graduating students who are not properly educated.

My personal, cynical take on this is that a subset of people in positions of political power realize that uneducated people are easier to manipulate for their own gain, and therefore deliberately support policies that have lead to the deterioration of educational standards. Additionally, business profits are maximized, at least in the short term, by maximizing the number of people living on the brink of bankruptcy. Every cent that the average person saves or invests or passes on to their children is a cent that is not being added to the billionaires' hoards. Less educated people are easier to manipulate into voting politicians who allow this to happen into power, which gives large corporations an incentive to help the aforementioned politicians get elected.