No, you do not have to write a cover letter for every job, but writing a cover letter can help increase your chances of getting hired.
If you’re really interested in a position, it’s best to write a cover letter unless instructed not to.
Tailoring your cover letter to each job makes it much more impactful than sending a generic letter. According to a ResumeGo survey, 78% of hiring professionals said it was easy to tell the difference between a generic and tailored cover letter, and 81% said they valued tailored letters much more.