GT program attendees aren't necessarily "gifted"
I am sure this will be uncomfortable for some but the title really says it all. For more context, "schools" are a system for build workers to varying degrees. Take this input and give us the expected and accepted output while fitting nicely with the lines. This goes for the social aspect too, learn to not stand out/or fit in with all norms and fads.
While there are programs for those on either end of the bell curve most funding and support historically has gone to the left tail. The programs offered to the right end did not serve enough individuals as the needs of those are much more difficult to understand or even see. This led to parents wanting their kids in the programs and a need for more students under them so the funding could be justified. Most gt programs do not have the same requirement for membership as "intellectually gifted societies". This is to say you need not have an IQ greater than or equal to 2sd above norm.
For reference please see gifted at risk, also school wide enrichment model. Many txt and interviews with SME's can be found further discussing the above mentioned.