Consider the practicality here. You can mandate a vaccination, because that is once, over and done, and documented. You can’t verify that your employee is daily, reliably taking ivermectin and vitamin pills.
The risk profile of Ivermectin is very, very well known, many billions of doses have been used over 40 or so years, the risk profile looks similar to that of aspirin or Tylenol. This vs. an experimental EUA mRNA therapy that has little history of good results with low side effects. Arguably the biggest experiment in the history of medicine.