But even secondary English teachers should be able to pass a mathematics proficiency exam.
Would we want barely literate folks teaching Mathematics? No, because mathematics does not exist in isolation. Someone who can't read and write reasonably well very likely can't teach mathematics in a contextually useful way. If someone cannot pass an English/French exam, I'm not so sure that they are literate enough to teach.
Similarly, a basic competency in number sense and Mathematical constructions is necessary to teach any subject, including English. If someone cannot pass a Mathematics exam, I'm not so sure that they are numerate enough to manage a grade book and interpret basic statistics about their students' progression. Not to mention teaching students how to write expository texts on technical subjects.
Remember: these exams are relatively low bars. We're not testing teachers on university mathematics; we're largely testing them on material they should have learned in order to graduate from high school in the first place. See https://mathproficiencytest.ca/#/en/applicant/learn/about:wh...