The reason is quality. Many smartphones have poor audio output quality. It’s all about the DAC (for digital to analogue conversion) and finding a phone you want (and can afford) that also has a good DAC leads people to invest in a stand-alone device. There are some LG devices, Sony obviously, but with phones dropping 3.5mm jacks they are becoming rarer.

If you look at the comparisons here you’ll also notice that the prices get up there. Now, once you go hi-res DAP, you don’t go back. I am a bit of an audiophile, but I’m also a cheapskate. When I finally decided to get an OK DAP I went for entry-level device and entry-level in-ear (hi-res) buds and now I realise that I was not, in fact, an audiophile because now I notice the difference between lossy and lossless audio.

Also, battery! I want to save my phone battery for phone stuff. My DAP lasts 7 or 8 days of going back and forth to work. Maybe more. It has a 20h battery. It also functions as a USB DAC, so I can plug it into a computer and it replaces the sound card so it is multifunction.