As much as the leftie in me wants to say we're not funding it, we are. Per-student, inflation-adjusted funding for education has gone up a full 50% in my lifetime [1], to more than $18k per student-year. $18k is a lot - for a classroom of 30 students, that's half a million dollars a year. We have the money, and indeed far more money than we once had, in a world where things are cheaper and easier. We should be able to do everything we did generations ago and then some. Sure, there are demands we make now that we didn't make then (like "maybe not with the asbestos", "kids with wheelchairs should be able to get places", and "maybe people with learning disabilities should get a chance"), but I have a hard time believing that those are adding >50% in real terms.
To me, the interesting question isn't the trade-offs, it's why we need to make them at all. It seems like we shouldn't.
The most appealing explanation to me is that there's a sort of low-grade hum of background corruption that is hard to detect but acting as a sort of friction on public-works projects. But that's hard enough to falsify that it's hard to be too confident in it, either.
[1] https://www.statista.com/statistics/203118/expenditures-per-...