Same happened with desktops, where this years chip offered no tangible difference to the OS usage feel and only high end processes were aided, motherboard upgrades the same, where much of a muchness with new connectors, throughput or bus options, memory improvements marginal, ssd's, so a new PC every year became two, became three, current build is getting on for four and I could replace it, but wouldn't notice anything but a hole in my wallet (and it's only a $500 AUD build to start with).
Then we moved to laptops, smaller, lighter, better battery, better graphics, higher res screen, now they two are much of a muchness.
So too with phones, the annual upgrades not delivering anything new in terms of battery life, camera, cpu/memory, my note 4 still does me well, it's thin enough, fast enough to do everything I need (plus I can still replace the battery and add an SD card). Yeah, a note 8 looks nice, but no, I don't feel compelled to upgrade as what I have will do, even with the built in obsolescence of turning off updates, when that happens (as I'm still getting them, but when) I'll just switch to one of the many open source, I know as I'm more technical then most others won't, but a wedge will sit without updates or noticing/caring, so only a small percentage will upgrade then.
We've reached peak phone, without something radically new (strapping to your face for poor mans VR or this year's hype wagon of AR don't count) they've progressed themselves into a corner.