Why dont people listen to 'retards'

Jesus christ. Why do so many people tune out the mentally disabled. It sickens me. 

I go to a pretty big highschool so theres a lot of faces, turns out when theres that many faces some of them might look a little different. Or might speak with a impediment/slur. THATS NO REASON TO JUST TUNE THEM OUT THO. Theres this one kid, his names jacob. Every lunch class me and my main group of friends will eat and yap, so far so good, then Jacob will come along once hes done eating (he sits at a diffrent table to eat) 

Hes always in such a good mood and has something to rammble about yet im the only person who gives more of an answer then a half conscious "hmm oh yea" speratically, obvious that its only to move the conversation, like skipping a cutscene or some shit. It hurts to see from an outside perspective since it seems like Jacob doesnt pick up on the fact there treating him poorly, im sure most people treat him (and others in similar shoes) like that so its the status quo. 

Theres many other problems with how my school treats their mentally/physically handicapped students (like literal sweatshop shit having them make most of the schools merch & running their snack booths (snacks and gum that the school sells throughout hall(s)) and making them leave the busses last for some reason even if there seated to get off earlier... 

Thanks for listening to my rant, first post on this platform so i still gotta customize all my stuff to look cool :3 gonna do that after school <<33