1) Learning multiple languages takes time away from learning other important concepts, skills, rest, and family time. Unless the job requires language translation, employers generally do not prioritize multilingualism over technical skills.
2) All people only have 24 hours per day, so time is precious. Learning an additional language means taking time away from learning other concepts.
3) If two candidates have equal qualifications except one knows two languages and fewer overall concepts while the other knows one language but more concepts, most hiring managers would choose the candidate with greater technical skills over multilingualism.