It's not as simple as hiriing vets. It's having techs to support the vets. Minimum, you need two techs to support a vet, ideally three. Many states require techs to be licensed and have at least AA degrees, so you're paying for an additional 2-3 educated people plus the vet.

Of course, the "ideal" rarely happens, the point is, with every vet you add, issues of juggling staff, scheduling, and turnover skyrocket