Yes, dealing and sometimes fighting with insurance companies is difficult. It wastes time that you could be spending massaging paying clients, instead of filing and refiling paperwork or spending long lengths of time on hold or talking on the phone to mindless morons who have no clue that their plans don't cover medical massage therapy. Been there, done that.
Then when the claim comes back as denied, good luck trying to collect from the client. The client feels that if the insurance is not paying, it must not have been medically necessary or appropriate. Some clients pay but are angry and never come back, even though the treatment was helpful. Others cannot afford to pay out of pocket.
It is difficult to know when to bill insurance and when not to. Some massage therapists just make it a practice to let the client bill the insurance and not mess with it.