In the US, much of a school's extracurricular program is funded via PTA, fund-raising, or simply charging extra fees. In this system, the well-to-do parents/families subsidize the others (poor students granted waivers to the various fees, or don't contribute to the PTA monetarily).
Given the strong correlation between academic aptitude and economic success, removing the smart students also remove the wealthy students. The funding model falls apart, and the students who remain get even less extracurricular enrichment.
Granted, we could design programs that mostly avoid the problem. In my county, the gifted high school (Thomas Jefferson High School for Science and Technology) only takes absolutely brilliant students. Many of whom truly fit the "too smart to fit in" stereotype. Across a large county, that still leaves plenty of gifted/wealthy students in the normal schools, which offer a broad selection of AP/IB/dual-enrollment options.
Given the strong correlation between academic aptitude and economic success, removing the smart students also remove the wealthy students. The funding model falls apart, and the students who remain get even less extracurricular enrichment.
Granted, we could design programs that mostly avoid the problem. In my county, the gifted high school (Thomas Jefferson High School for Science and Technology) only takes absolutely brilliant students. Many of whom truly fit the "too smart to fit in" stereotype. Across a large county, that still leaves plenty of gifted/wealthy students in the normal schools, which offer a broad selection of AP/IB/dual-enrollment options.