Well, I think it's as simple as you say. Phones have completely taken over the market. The majority of people don't find any value in having another device that's only differentiating factor is that it isn't their phone. (You didn't mention headphone jacks).
It's just like portable GPS devices, electronic organizers (https://www.youtube.com/watch?v=qdeE_kiG5Co), electronic translators/dictionaries, calculators, alarm clocks, ...
It's just like portable GPS devices, electronic organizers (https://www.youtube.com/watch?v=qdeE_kiG5Co), electronic translators/dictionaries, calculators, alarm clocks, ...