Another reason that a student may not take calculus in high school is that the student’s math placement in middle school did not put him/her in the +1 or higher math track that allows taking calculus in high school.
Many high schools do not offer calculus, but it is unclear what percentage of students attend high schools that do not offer calculus. The usual number is 50% of high schools in 2014 do not offer calculus, but that is based on the set of high schools that includes continuation/reform schools, juvenile hall schools, etc… Such high schools may have small enrollments of low performing students, but each such high school counts as much as a larger general high school.