Honestly, I think it's the always on cellular internet connection.

I had a Palm back in the day, flashed it to Linux, had a web browser and could get WiFi through a Cartridge that looked like a Gameboy Advance game. The whole setup was bigger than my phone is now, and only made any sense at all because, at the time, I was living near a campus where wifi was everywhere.

I had the old Nokia unbreakable phone and that thing with me at all times. Each one weighed more than my phone does now, and together they were 1/10th as capable, but putting the two together was what changed the game.