Do orthodontists always prescribe bonded orthodontic retainer? my family member wasn't prescribed one?

Not always. A retainer can either be fixed or removable.

There are many retainer designs, some fixed, some removable. Each has advantages and disadvantages, like any medical device or medication. The decision as to the proper retention protocol is individualized based on the patient's original malocclusion, patient cooperation, and the Orthodontist's training and experience, not what someone else needs. Use exactly as directed to promote stability.