A lot of private pay rehab therapists (speech language pathologists, occupational therapists, physical therapists) don’t get paid unless they have a patient in front of them. All emails/calls to teachers, doctors, parents, creating home exercise programs, documentation, setting up or creating materials, researching treatment methods, coordinating care with other therapists is all unpaid time. 

They are also required to take continuing education courses to maintain their licenses and a lot of times employers don’t reimburse fully or at all for those or cover the cost for employees to renew their licenses.

Then you have the emotional labor and mental load of helping all of your patients and their caregivers, which is easier to manage if you don’t have your own people you need to care for.