Why are visual or performing arts in high school not considered "academic" by many around here?

Example posts:

Regular History or AP CS Principles? - #7 by Ohno2 (#7 and #8)

Journey of a low gpa/high score/not typical excellent CC kid (warning: long post) (#1, “2 VPA electives senior year (along with 4 core academic subjects + compulsory gym class) whereas I felt they should have “caught up” on a missed academic elective”)