A business needs an app when people repeat a job that a website handles badly: something they do often, often away from a desk, or with the phone’s own capabilities. Ordering, field work, and a daily operational task are common examples.
It is a weaker sign if the only goal is “customers expect an app” and the website already does the job. An unused app is a second product to maintain.
Write down the job, how often it happens, and what is painful on the current site. If that sentence is hard to finish, stay on the web a little longer.