One of the main issues with any crypto, is the need for the internet.
Typically this is land based, and in those areas lacking data connections or phone lines it can be difficult.
Merchants however are typically in built up areas, and may have internet, at least on occasion.
But BTC now has a new Airforce, by utilizing satellites, connections can be made anywhere on the planet (maybe the poles excluded).
Why anyone in a remote are would have a smartphone, is unclear, unless they only use it when "in town", but merchants probably do, so they can accept BTC from customers.
https://www.newsbtc.com/2019/02/08/will-offline-transactions-be-the-next-evolution-for-bitcoin/