This is rather out of the blue, but I honestly speculate that Bob and Barb's black-and-white, oversimplified understanding of psychopathology must have been the foremost reason why they completely denied the need for the special education for Chris.
From the fact that Chris was already publicly known as "With High-Functioning Autism" in his Sega Sweepstakes news in 1994, I guess that there must have been an official meeting between Borb and the local doctor where the doctor finally mentioned Chris's diagnosis for the first time - I actually speculate that, when he finally faced the situation where he needs to explain the diagnosis of high-functioning autism in the way that the old couple is able to understand with ease, the doctor explained it as 1) Chris does have autism 2) and yet his IQ is normal.
There is what I think things got completely wrong since, as far as I may speculate, Bob and Barb amplified the "his IQ is normal" part out of proportion, even while the doctor's original intention must have been focused on the "he still has autism" part instead. As soon as that unfortunate amplification happened in Borb's heads, Chris was deemed "neurotypical for no doubt" to the old couple. This can certainly happen if I were correct with the assumption that Bob and Barb had extremely binary and oversimplified understanding of psychopathology, which often makes these people view this subject in the binary of "neurotypicals vs TARDS" - Historically, before it reached the late 19th century, even a lot of government-managed asylums could not make a clear distinction between schizophrenics and the mentally rэtarded.
Assuming that Bob and Barb lived most of their lives in unfortunate environments where such incorrect binary has not been updated yet, and if I were correct with this assumption, it should be deemed kinda inevitable from the beginning that Chris would be denied of all the resources prepared for him out there by his own bloody parents.
