IMO you kind of do get spaced repetition in modern education. As you specialize, you frequently have major classes where its "first week or two we dig into what you already should know, then we really dive into the deeper stuff." Or you take up a job, and maybe you have to refer to that one topic from class years ago twice a year, that's spaced repetition.
In a sense, the nature of a specialized career forces you to engage in spaced repetition of the things you need to know, and allows you to safely ignore the stuff you never need to touch again. If we encouraged spaced repetition on each and everything, I would be wasting a ton of time on subjects that ultimately aren't relevant, at the expense of free time and maximizing time spent on the relevant bits.
This is the perspective many people have, but in my experience it falls short. To quibble with your examples:
> As you specialize, you frequently have major classes where its "first week or two we dig into what you already should know, then we really dive into the deeper stuff."
Yes, they do this. But I've often seen (especially at the undergrad level) instructors avoiding topics or challenging problems because it required material beyond just the basic math/calculus (e.g. some trig identities, differential equations, etc). So in practice, this is not happening.
> Or you take up a job, and maybe you have to refer to that one topic from class years ago twice a year, that's spaced repetition.
It's even worse at work, where you don't have a teacher to enforce things. Suggestions get shot down all the time because coworkers have forgotten some (even trivial) things they learned at university, and they do not want to review it. I've seen this happens where they avoid basic Calc I stuff, where they avoid stuff in data structures (e.g. union find). They'll implement a poor solution, and convince management it can't be done better. Or that it can but it's a long term risk because if that one person who knows "union find" leaves, we won't be able to hire someone to maintain it, etc.
> If we encouraged spaced repetition on each and everything, I would be wasting a ton of time on subjects that ultimately aren't relevant, at the expense of free time and maximizing time spent on the relevant bits.
Michael Nielsen did an analysis of this after using Anki for a bunch of years: The average amount of time spent on a card over one's lifetime is about 10 minutes. And so he used that as a metric when encountering any new piece of information: "If I don't learn it, do I think I will spend more than 10 minutes looking it up in the future?" If yes, he'll make a flashcard for it. If not, he won't.
But yes, I definitely have disabled cards on topics that I don't think I'll want to touch again in the future.
In a sense, the nature of a specialized career forces you to engage in spaced repetition of the things you need to know, and allows you to safely ignore the stuff you never need to touch again. If we encouraged spaced repetition on each and everything, I would be wasting a ton of time on subjects that ultimately aren't relevant, at the expense of free time and maximizing time spent on the relevant bits.