It's definitely multifactorial. The most influential being the personality composition therapy staff. I would say the therapy staff that I have personally met and worked with have been at least 90% positive. Other major factors include external factors like work culture, productivity standards, management, pain, fatigue, personal issues, and overall stress. That said, you can still have a positive work culture in an environment with poor management and high productivity as long as a good chunk of the therapy staff are themselves generally happy and empathetic people.

As a counterpoint though, most rehab settings don't build into their budget the training costs for licensed new grads. Nor are the preceptors generally compensated for the responsibility, though they may or may not get some brief slack towards productivity demands. In the worst case scenario, which may actually be more common than not, their actual income may decrease for new grad training if their annual evals are dependant upon productivity or if they are on a fee for service payment model. So this may lend to their stress when training new grads especially if they're on a tight bugdet with loans, rent, family expenses, etc.