Doorknobs are much harder than lever type handles for people with arthritis or similar conditions to operate (since they require gripping firmly, as opposed to just pushing). However in some areas where bears are a threat, doorknobs are mandated since bears have been reported to have learned how to open lever handles (but either haven't learned or lack the dexterity/grip strength to use doorknobs), so knobs are safer.

Also, anyone with a helper dog. You can tie a small rope to a lever, but not a nob. So the disabled can rent without having to change out all the nobs/locks.