AP courses are reviewed and approved by college faculty to make sure that every student who takes AP is being asked to do college-level work, no matter where they take it. AP Exams are a standard way to measure how well students have mastered the college-level subject matter. Colleges across the country know this, and many grant college credit or advanced placement to students with AP scores of 3 or higher.
Dual enrollment programs don't offer a standard way to measure whether students have mastered college-level work. Because of this, it's difficult for college admission officers to know the quality or difficulty level of any dual enrollment course.