There are websites that allow you to buy ETN with fiat and also some exchanges. Liquid is one I believe, Richard Ells has responded to this question in the past and has said allowing people to buy ETN through the app or in someway would be extremely difficult to setup and require lots of regulations be met in hundreds of countries as ETN app is used world wide so in each place they would need to support a payment system.
He never said it wouldn’t happen only it would be very difficult to setup. Also generally speaking cryptocurrencie teams don’t usually let you purchase there coin through them directly with fiat for a few reasons it is generally done through exchanges or other services/websites. That is why they have the mobile miner to make it easy to get a small amount of the coin but its not really aimed at western countries.
You can check out this thread here which lists places you can purchase ETN using fiat - Fiat Listings for ETN + Debit/Credit Card Option
