Why do doctors refer to sleep disorders if most advice ends up being hygienic, shouldn't this be treated medically? or is that not often possible?

"First, do no harm" : is still part of the Hippocratic oath we take. A careful history and physical may reveal the source of delayed-onset sleep or early waking as stress- or habit-related rather than sleep apnea in adults. Pills don't teach skills; learning what stimulants a person takes, diagnosing depression & teaching good sleep hygiene are important steps before prescribing potentially harmful medications.