I mean....a part of the problem is that the Psychonauts kind lives in a world of jerks, where everyone is just a jerk for no reason other than comedy. like they're recruiting that one kid who is cruel to animals and expecting her to like, respect the minds of PEOPLE? Not a reasonable thing in a sane world. or take the fact that none of the kids give any respect to Raz despite him being basically a child prodigy at this point, at either the camp or at the base. people in the world of psychonauts are just kind of jerks all the time, not exactly a good environment for getting better.

there is also the fact that two of the psychic six are these isolationist people clearly more comfortable talking to bees or animals than people. Cassie and Compton both seem highly telepathic and its modern trope that people who are strongly telepathic can "hear" too many thoughts and experience sensory overload because of it, that telepathy is only a good power in moderation when you can focus it on one mind. this in particular prevents them from receiving help because to get it they'd have to go to among more complex thoughts which seem louder than just animals.

Helmut, its obvious why he didn't receive help, he nearly died and got put in a tank- funnily enough his brain is actually one of the healthiest of them once it gets over the sensory overload issues, which is Raz inflicted, while coming to terms with the memories is one of the easiest parts in the game it seems like, so it seems if got the chance he would've had the help he needed to move on.

Ford implies his own mind shattering was self-inflicted, so he probably set up defenses to prevent people from fixing him- his condition may have been less bad in the past and his mind stronger than but his defenses only deteriorated with time as his mental state did. Then he went off to live at a psychic camp, so of course he didn't get the help he needed, he was busy being the janitor to brain camp for young psychics.

Otto Mentalis seems to be a mad scientist kind of deal no matter how good or evil he is-he might get stuck on long projects without really talking to anyone because he is focused on his work that no one else really seems interested in helping out or understanding what he is on about. Thus it is its own form of isolation.

While the sixth member, we haven't seen yet but given that they aren't around, they're probably isolating themselves as well.

In short, one of them was on brain life support for decades and the other four-five of them are deliberately isolating themselves in their interests rather than deal with people. they just all collectively decided to hide in their little turtle shells as coping mechanisms rather than risk screwing up a mission because they had been mentally compromised. Milla, Hollis and Nein seem more mentally balanced, Oleander just seems to be kept around because its probably better than letting him wander off to screw up something. also the Psychic Six were the ones who did the whole psychic pioneering experimentation stuff that lowered their mental defenses- perhaps their cases took more time to heal because of it, while most psychonauts having learned from their "frontier age" of psychic powers put safer and more reliable methods into practice, which is why you have a bunch of nameless probably more mentally well adjusted psychonaut agents in the motherlobe around, they're just....not important to the plot, so they don't get a name or the ability to participate.