US public education spending as a percentage of GDP is lower now than in 1993:
https://ourworldindata.org/grapher/total-government-expendit...
Why should it scale with GDP? GDP growth represents more goods and services produced.
If GDP doubles and you go from $1 eggs to $2 eggs, GDP didn't actually grow or you are being swindled.
Expenses for a fixed goods and services should decrease as a percent of GDP over time. If they don't, that means spending is less efficient over time.
The percentage of children in the population is lower than in 1993.