What you wrote about I absolutely agree with your point of view, But I can think of one or two reasons why / who wants a dedicated DAP.
(1) People with lots of High Res format (DSD, ALAC, FLAC, WAV, APE) Audio purchased/collected from different sources and want to carry them on the go or access them off the desk...i,e without any Computer...Zero faith in Lossy format despite their hearing capability.
(2) The above category people usually own a single or more than one very very high-end expensive IEM, they are absolutely satisfied and realized as their end game, Don't want to use any Full-Size headphone / not interested at all / not like to do any experiment.
(3) No expandable memory at their phone / too hard to transfer all those music collections/ Don't want to clutter their phone....Not much faith in Music Streaming and want to Physically / Digitally own their music.
(4) A large collection of Physical format at their home from the early days from the pre-digital era.
EXACTLY.
Also for people with LDAC or AptX HD DACs, speakers or headphones that cannot transmit bluetooth signal with this quality from their phones/tablets/computers...
my case indeed haha