The kind of high school that has visits from test-prep company speakers is the kind where students are expected to treat “recommended” subject tests as “required”. The kind of high school that may have a handful of graduates go on to a four year college or university is the kind where students may not have heard of the subject tests before it is too late, and which colleges or universities that “recommend” subject tests may be more understanding if a student from there does not have them.
UC says on http://admission.universityofcalifornia.edu/freshman/requirements/examination-requirement/SAT-subject-tests/ that subject tests are recommended for applicants to:
UCB: College of Chemistry and College of Engineering
UCLA: School of Engineering
UCSD: School of Engineering and science majors