The problem is just bad planning. Smartphones aren't always designed for high fidelity audio. Telephone quality is very low and a chunk of the circuitry might be designed with that in mind. Then they graft a high fidelity DAC onto it and the phone circuitry becomes a bottleneck for whatever reason. It's the same with computers. Not all computers come stock able to reproduce sound to a high level. They figure for the purposes the computer is designed, high fidelity sound isn't needed. Then some marketing expert can decide "All computers have sound- let's stick a sound card in." and it doesn't sound good. It might not even be the sound card's fault- RF interference from bad shielding, that sort of thing can mess up something that would be audibly transparent if you put it in the right machine. That's why phones and computers are always the first thing I suspect when someone is saying they aren't getting great sound out of their amp or headphones. It's also why I use Mac computers and phones. From the first model I owned capable of sound, the 8500 AV, Mac has had perfect sound.
Home audio equipment like DAPs, amps and dedicated DACs are designed specifically for high fidelity sound. The spec for 16/44.1 PCM is complete audible transparency. If something is able to meet that spec, it's going to sound just like everything else that meets spec- as good as it gets for human ears. You can get better performance, but you would need that in a recording studio, not a living room.
I have yet to find any consumer DAC, DAP or player that isn't audibly transparent. That isn't to say it doesn't exist, just that it probably is rare enough that you don't need to worry about it. If you buy a computer or phone, you probably should check into the sound quality before buying though.
Does that answer your question?
EDIT: I just thought of one exception to not having ever found a DAC that wasn't audibly transparent... NOS DACs. They have a high end roll off to make them sound "warmer". For the life of me, I don't know why anyone would buy one. You can do the same thing by just adjusting your tone controls without deliberately hobbling your DAC's performance. But some people have weird ideas about what they want.
It does and it raises even more questions in my head. I feel like I'm gonna regret this since most of my listening career would involve cheap DAPs and Chi-Fi IEMs but I'll go ahead and look up what does what in an audio device. No information is bad information afterall. Thank you so much!