1. Its difficult for the average phone user to be convinced to spend money on a device that would cost considerably less if purchased outside the country.
For example, someone was telling me (I haven't personally validated) that its cheaper to take a flight to Bangkok, Thailand and pickup a Macbook Pro 15' 2018 and get it back than buy it in a local store.
The same thing holds true for iPhones as well. A lot of people get phones from friends / family traveling to other countries as its cheaper to buy there.
2. Android phones provide a lot of options at a variety of price points. The choice is ultimately the reason most people go the Android route. In case of Apple, only the iPhone SE is priced in a reasonable way (as the article points).
3. You don't get the same experience buying a iPhone as other countries as Apple does not have flagship Apple stores. The sales happen through re-sellers. That could be a factor as well.
4. Broadly expanding to other Apple products, the clear lack of choice puts people off. For example, I really want to buy the Macbook 12' but with a upgraded 16 GB RAM. But that option is not available on the online store or with the reseller.