It's a problem with anything chronic or long term. The people still have the problem but their support suddenly disappears because they magically transition overnight from a child, who in America at least have some marginal bipartisan support for helping, to an adult, where assistance is much more fraught and spotty.

If compared to physical disabilities, Autistic sufferers are sometimes a lot worse off as their symptoms are not visible. Convincing the social services becomes quite difficult.