Audible makes the strongest early shortlist for people who actually finish audiobooks often enough for a membership structure to make sense. Those are the users most likely to feel the service's strengths quickly rather than having to talk themselves into them.
The opposite test matters just as much. Audible is usually a weaker first choice for people who only buy the occasional title and do not want an ongoing monthly relationship with the service. That does not make it bad; it just means its strongest arguments are aimed somewhere else.