It was the same thing when I was a kid in the 90's and I was bored out of my mind at school, completely and utterly un-challenged. I can barely even put into words how bitter I got about being dragged through such a system. There was no such thing as "advanced" classes, and the only so-called advanced stuff I ever did was outside of school in special programs, which I'm pretty sure my parents had to pay for me to participate in. It was a parent-created/run organization.

Anyway, to answer your query, my belief after decades of observing the education system here (BC, Canada) is, politicians and decision-makers basically feel that smart kids have a huge advantage and they don't need the help. They will succeed and be useful members of society whether we leave them for dead or help them thrive. So... the dollars can be allocated to "those who really need it". I have heard this overall sentiment shared over and over and over, as far back as when my parents and I attended city council meetings appealing for ANY sort of "gifted" program implementation, even a tiny hint of one. The answer was always "find a private school", "I heard there's this virtual school you can attend on the computer", "we'll think about it", etc. I honestly don't see this changing anytime soon.

I could say way more on the subject but didn't feel like posting much more of such a personal topic. Happy to chat about it more with whoever, though.

In California, “we” decided this in 2014, when the state did away with mandatory GATE requirements for districts. It’s now optional, and schools aren’t doing it.