What would it even look like for education to be “solved”? I think if you put 10 people in a room and asked them what the purpose of education was, you’d get 10 different answers.

A good education is not being provided to every child who is in need of one --- that happening would be a solution to the problem of education, that it does not, is the problem.

It's mostly an socioeconomic problem, at least for US public education. People don't want to pay for other people's kids.

How to get great educational results is to have a good teacher, or, better, a good individual tutor, and, most importantly, a good student. Also, there are some techniques that help, but those don't matter very much by comparison to how good the teacher is, whether they're teaching a class or an individual, and how good the student is.

There are three reasons this doesn't make education a solved problem:

1. Often, students are not interchangeable, in the sense that the problem we are interested in is how a particular person can get educated, rather than how someone can get educated. So knowing that the quality of the student matters most of all doesn't give us much of an attack on the problem, at least after you solve the obvious problems like iodine deficiency, lead poisoning, kwashiorkor, starting classes at 7 AM, and your best students getting sent off to death camps. Even these are often out of the control of the would-be education reformer. So "have the best students" is the most important thing we know about how to get great education, but it doesn't make education a solved problem.

2. It's difficult to tell which teachers or tutors are good, partly because student quality is so much more important than teacher quality (so a single particularly good or bad student can make a teacher appear particularly good or bad, an effect that is even larger for tutors, and overall student populations are also variable, for example because of admission requirements or brain drains), and partly because the bad teachers and tutors have strong incentives to fudge the signal. Generally speaking, those running educational institutions are drawn from among the worst teachers, compounding this problem. So, although "use the best teachers and tutors" is a thing we know about how to get great educational results, but when we don't know who the best teachers and tutors are, it doesn't make education a solved problem.

3. There aren't enough really good tutors to tutor more than a tiny fraction of students individually, so even if you can get the best tutors to teach (forbidden by law in many places, for example by teacher-licensing requirements, and often economically unappealing for the tutors) you're still left with the important question of what to do with the majority of the population. So "tutor individually rather than teaching a group" and "use really good tutors" are things we know about how to get great educational results, but it doesn't make education a solved problem, even when we know who those tutors are.

4. Plausibly, there is some way that we could still get much better educational results than the best tutors tutoring the best students today. Many of the things that students today do to improve their educational results, such as consulting Wikipedia, memorizing vocabulary with spaced repetition systems like Anki, or reading books, are things that were not technologically possible at some point in the past.

None of these problems are a result of people not caring or actively hating the solutions.