A student recently asked me if you had to be a physician to be a medical writer. The answer is no. Opportunities in medical writing are vast. If you want to write and be a lifelong writer, then you can excel in this field as a nurse, a PhD, a PharmD, an MD/DO, or even an MS in biomedical writing. Some medical writers also do really well with a BS or BA in scientific journalism or biology. You'll have more opportunities if you have an advanced degree, but it's not a requirement to be an excellent writer.
Keep in mind that many clinicians may start out writing, but then they advance into other senior positions that may involve project planning, team management, company strategy, new business development, etc. Others love to write and that's their passion, so they have no ambition to do anything else.