One problem with dual enrollment is that it’s actual college – and it usually involves a college that isn’t particularly impressive, academically, such as a local community college or directional state college.
Highly capable students who take a lot of dual enrollment courses get a large chunk of their college education from colleges that are not very rigorous. They also enter full-time college as upperclassmen, not freshmen, which means that they miss out on the typical college experience that many young people value.
So ironically, what happens is that extremely capable Jane ends up taking half of her college credits at a community college while she’s in high school and then enters X university as a junior and finishes up her degree in two years. She never really becomes part of the X university community because she’s there for such a short time. She also doesn’t fit in well with the classmates in her upper-division courses because she’s younger than they are (notably, she can’t drink legally and they can, which is even more of a problem at that age than R movies and driver’s licenses are for accelerated students in high school). Meanwhile, slightly less capable John, who doesn’t take any dual enrollment courses, goes to the same university in the normal manner, gets a more rigorous education, and has a better social experience at college.