Good question, and there are couple of reasons why people buy the import feature.
(1) If you are switching from Android to iOS or vice verse, app can make the contact transfer process very simple and convenient.
(2) People like you and me can find very easy ways to transfer contacts, but there are a lot of non technical people who don't know about auto backup and restore features.
My app makes roughly around $1K/month. A simple utility to backup(free) and restore(paid, in-app purchase) mobile phone contacts.
Check it out: http://c2x.eastros.com/
Experienced Backend Engineer, love to do everything that happens on the server side, including architecture design, data modelling, business logic implementations and rollings this out.