What would be reasons for intelligent people with autism to particularly struggle once they hit college?

In posting and following subs such as this one, I've seen a plethora of stories of those with autism who either didn't finish college or had to grind at it to get a gpa between 2.0 and 3.5. And not unintelligent students either, and yet college for the majority seems as though it was particularly trying.

What are unique reasons who intelligent students with autism would struggle more in college? And find themselves more overwhelmed than they were in school before? Lack of structure and trying to absorb too much at once? An isolated environment, senses being overwhelmed? Or perhaps other factors?