Because it's heavy, large, battery life sucks, breaks when dropped, might not even have a 3.5 mm jack and most of all requires me to look at its display to do anything.
I have one of those Sansa Clip players running Rockbox that I use for sport and bike commute. It costs nothing, it is virtually indestructible, has more space for music than anyone ever needs and I can operate it without ever taking it out of the pocket its in. Simple physical button presses to start, shutdown, resume last playback position, adjust volume and move forward and backwards between songs and folders.
Charging isn't an issue, it lasts days and days. I don't actually remember the last time it ever ran out. Not mention I use it as a handy sub storage for other files. It's ultra light, and as someone who does a bit of running I'd feel ridiculous having one of those arm patches to hold a £xxx phone.
I have one of those Sansa Clip players running Rockbox that I use for sport and bike commute. It costs nothing, it is virtually indestructible, has more space for music than anyone ever needs and I can operate it without ever taking it out of the pocket its in. Simple physical button presses to start, shutdown, resume last playback position, adjust volume and move forward and backwards between songs and folders.