- smaller devices reduce shipping costs en masse
- marketting "thinner" devices (though screen is larger?)
- DRM
- No need to provide expensive native DAC
- Owning the headphones market, similar to how google ended up owning "search"
I'm sure there's a bunch more. It makes good business sense for them regardless of what customers (ahem, "consumers") want and with other manufacturers following suit they'll pretty much have no choice.
I'm looking forward to a portable DAC being among the collection of crap I have to put in my pocket in the morning.