Firstly because they could have special schools for sign language. I think they should have special sign language schools because then other people don’t have to learn it as well. Because that might be not very good for people deaf because it might take some time away from their reading, writing and other important lessons.
Secondly because not everyone is deaf. Only 4 in ten people are deaf these days so it is no need for an extra class. They could have the class in high school but you choose if you want to do it or not. That would be better than you have to do it.
Finally because they could do without it at school. The people that are deaf can learn it at home or at the hospital. They don’t have to have it at school if they don’t want to.
I hope you are on the same side as me.