UCR CHASS policy against switching out

https://chassstudentaffairs.ucr.edu/transition_advising/index.html indicates that students in CHASS (humanities, arts, and social sciences) who want to change into CNAS (natural sciences) or BCOE (engineering) must be be eligible to do so in the first year.

So a second year student who is eligible to change into a CNAS or BCOE major according to those divisions’ requirements ( https://cnasstudent.ucr.edu/majors/ or https://student.engr.ucr.edu/policies/requirements/majorchange.html ) would not be allowed to do so by CHASS policy.

This seems odd, since usually restrictions about changing major or division are about changing into the new major or division (due to capacity limitations) rather than out of the current major or division. What is the reason for this policy?