superscore policy

Here’s something I don’t understand about superscoring. Many schools will superscore the SAT but not the ACT. Is there something in the very structure of the ACT that makes superscoring that test different than superscoring the SAT? Or are the admissions officers just lazy and are only willing to add together 2 numbers from 2 different SAT’s, but are unwilling to add together 4 numbers from however many ACT’s are taken?