Originally Posted by Silentwolfdog

Here's a few reasons for this.

Poor education system. (My school was like this. The system was messed up and as results we suffered.)

They learned ASL far too late at this stage. (Best time to learn language is when you are born, not 5 or 6 years old.)

No motivation. (I remember I was the only one out of my class that really tried to do homeworks, studied, etc. and yet none of them seem to try. They blamed school when they did nothing to help themselves as well.)

They come from poor family background. (Can you really focus at school if you were abused or neglected by your own family member?)

That's only thing I can think of right now. I am sure there's more reasons for what you have asked.