The killer feature of CD players is shuffling and skipping tracks.
Heck, it used to be all the rage to get a three or five CD changer and shuffle the whole thing, comfortable unpredictability, forty or fifty songs you like but never knowing which is next.
You could likewise just listen to an album on your phone, in order, but it's too easy to let your distraction kick in and switch it halfway through.
As someone who grew up during the transition, the killer feature of the CD was amazing audio quality and the lack of degradation from every playback. The period where we started finding albums marked "DDD", for fully digital production, was also amazing.
It saddens me a little that, in spite of all the technology, actual Hi-Fi listening seems to have become less accessible or prevalent. I'm still not sure how much this is really for the commonly stated reason of convenience, and how much that is really cope and denial of a bigger socio-economic decline. I.e. it simply isn't as realistic for regular people to have a Hi-Fi listening space...
Anecdotally, I don't think hi-fi's decline has to do with cost - at least not cost alone. You can still get a more than decent system which will fit most living rooms for quite reasonable money - I just had a look at prices at a national retailer's website here in Norway, and you can get a pair of decent bookshelf speakers and a stereo amp delivering 2x60W into 8 ohms, built-in streaming support and a HDMI input to ease connection to the TV, covering the most common use cases nowadays, for less than $1,000.
For comparison, median income after taxes is approx. $50,000 a year, so we're looking at less than a week's net wages.
I think it is more likely that our media consumption habits have changed - when I was a kid in the eighties, a few - like, the bank branch manager, the dentist and a few others - had a VCR at home. The rest of us had TVs, meaning we watched what was on at the time, or (once in a while) rented a VCR and a movie.
That aside, our media choices were radio, going to the cinema (not very often!) or - drumroll - recorded music.
Hence everybody had stereos. I believe my parents were quite typical - when I was a toddler, they bought a number of LPs with radio dramas for kids on them, music for kids &c - the stereo was basically the entertainment hub.
Today my family and I - wife and three kids aged 10, 12 and 16 - have between us, let's see, 2xTVs, a 40" and an 85", the latter with a 5.1 system attached, both with Apple TVs, a stereo (making us an outlier!), three ipads, three smartphones, two dumbphones, a handful of radios, three - oops, four - laptops, a PlayStation, a couple of Nintendo Switches...
There's basically so many more options to spend our media time on, and at the same time there's way more leisure activities aimed at kids now than when I was a kid, so the kids are barely at home during the week (at least it feels that way!), leaving less time (methinks) for media consumption than only a generation ago, while at the same time having many more options.
So - basically, for many, only a generation ago, the stereo was the entertainment hub and you were kind of expected to have one. Nowadays the entertainment hub is some kind of internet-connected device, and a stereo is a niche product.