Not all PE problems are existential; they will be outcompeted. What keeps a newly graduated Veterinarian from opening her own clinic and undercutting the PE competition? With no massive loans on her books, she can profitably offer lower prices than PE can. She may even drive the local PE clinic out of business.
Except every newly-graduated veterinarian does have a massive loan on their books, in the form of student loans. And even if she didn't, where does the startup capital for her clinic come from? Whether in human or animal medicine, starting your own practice--especially as a new grad--is usually the course of action with the highest-risk-to-lowest-pay ratio.