Maybe because they want to (re)take the equivalent classes of the AP credits to enforce the knowledge.
My D graduated EECS in 3 years. She was granted 21 (or 27, I don’t remember the exact number) AP units. She also had about 30 units of college-level (above AP level) math and physics from Stanford EPGY, which were evaluated to comparable classes by UCB Math Dept. and Physics Dept… But CoE didn’t allow those units. She however could use those to petition to take more advanced Math and Physics classes instead of the basic required classes.