Re: "It just so happens that there's something better."
It took MP3 to replace cassettes -- a format that was cheaper, more convenient, and more portable.
Cassettes were Good Enough for most people.
4G is Good Enough for most people. 5G holds no draw for me.
They didn't really aim DAT at the consumer market - it was aimed at the semi-professional (or professional) who wanted a high quality medium without paying full-whack professional prices. For domestic uses, CD very quickly replaced vinyl, and except for home recording and some portable (Walkman) uses it also replaced cassettes, and this because the quality and convenience were so much better that people accepted the price - and the price quickly dropped.
For a while DAT was actually relatively good value for money if you were doing - say - field recording. For considerably less cost than the typical analogue Nagra you could get an hour of digital stereo onto a small and robust cassette.
Nevertheless, many outfits didn't even need that. The reporters at the local radio station I worked at in the 1990s were still using cassettes, albeit with Marantz units similar to these which we had modified to take balanced microphones. Among several advantages over a normal cassette recorder was the curious double-flywheel drive system. Two counter-rotating flywheels helped to keep the tape speed constant even when slung over a reporter's shoulder and knocked about - something that the helical scan head of DAT really struggled with - and rather than buying cheap 90 minute cassettes we had cassettes holding 10 or 15 minutes per side made from the exact same tape used in our ¼" reel-to-reel machines, slit down the middle by the manufacturer, Zonal. Robust and perfect for voice.
When I went to record a baritone at Llandaff Cathedral or a carol service at St Woolo's or a male voice choir in a local sports centre I used a DAT machine - albeit one which belonged to the presenter, as the station was too tight to buy one and would probably have suggested I sling a Revox in the back of the car if I wanted something better than cassette :-)
Your point is just as valid though if you consider the things that were supposed to supplant compact cassettes - Minidisc and DCC. Both were too expensive compared with "good enough" CC and while MD vastly improved on the convenience (the discs were random access, easily re-recordable and very robust) DCC most certainly did not.
It doesn't work in quite the same way with mobile phones though. To be perfectly honest, many people could get by quite nicely with GPRS data and 2G for calls & texts (remember, for example, that Twitter used to work via text messages), though 3G and particularly HSDPA does make web browsing on a typical bloated site much more pleasurable.
Unlike home recording formats though, mobile phones tend to have a high turnover rate. This is changing, slowly, but if you are on contract you will more-or-less automatically get a new phone every two years (or whatever). Someone on a 4G contract today might well have a 5G capable phone next time, whether or not they really need one. Even those not on that type of contract will be looking at (at best) a three to five year lifespan - mobile phones have a hard time of it and it's often more economical to replace a four year old phone - which might also need a new battery - than repair a damaged screen.
I have a six year old Moto G and I'm probably going to have to replace it this year. I really don't need anything more than a solid 3G data connection but I can 100% guarantee that my next phone will be 4G, and if it lasts 4 or 5 years the phone after that will be 5G.
Not because I need it or want it or am keen for the latest-and-greatest, but because by the time I get around to buying my phone-after-next, 5G will be there by default. Probably.