It may be one of those things like Fastpass time enforcement. GAC was supposed to tailor the benefit based on need. Over time, I think that they just got lazy and decided that they would just send them all into the Fastpass line. If there was no reason why a person couldn't be in the regular line, then that is where they would go, as it was designed. If they had a problem that prohibited them from being in crowds or waiting long periods of time then they would make exceptions on a case by case basis. That's how it was supposed to work anyway. They let it go, and perhaps now they are trying to do it the way it was designed. Or, who knows! Could be any reason.
By just automatically putting them through Fastpass, it opened it up to a huge potential abuse problem. ADA says that you cannot ask for proof of a handicap, so therefore all anyone had to say was that they needed a GAC card and, just like that, you have a permanent Fastpass to everything. Now they can ask what "special" needs they have and that is how it is tailored for each individual.