the only reason I could think where it might be is if you are being supervised and your illness is not well managed, or if perhaps if you are undergoing therapy as a requirement of your degree program and maybe there are some serious concerns. perhaps there would be reporting requirements. I am not sure but it makes sense to me....

there are other careers where your health impacts the career so this does not appear to be so strange to me. some require blood/urine screenings for drugs/alcohol, it used to be cdl drivers could not be using injectable insulin, law enforcement officers might not want to be schizophrenics, etc. yoi don't want your brain surgeon to have hand tremors...etc. so if your therapist has some form of severe mental illness that impacts their judgement, perhaps they should look elsewhere. perhaps overall it isn't required (again I don't know all requirements for programs) but common sense & judgement should play into action here.