I used the OnePlus One way past its EOL. Replaced battery and screen multiple times, custom ROMs based on linageOS tuned by the community to revive important features like RAW, 60s Shutter Speed and introduce some new ones not unlocked by the OEM, like manual focus. This included firmware modifications of various subsystems to improve the QoL, like introducing Stereo Playback via the speaker and tuning the Speaker curves to sound acceptable.
There is a lot that can be done and there is a lot that people do.
That's only enthusiast do in developed world. I'm curious does poorer people in developing world uses alternative ROMs. Is there any store that supports ROM flashing?
We'll never be able to judge that from the POV of our fast moving first world tech sphere and it's one-time use consumerism. That makes it all the more important to keep those options and avenues of modification not only alive, but strong.
As individuals we can of course offer mere anecdotal evidence. Coming from Belarus, I can say that the amount of talented hackers repurposing old tech was always strong there, though I don't have a strong connection there anymore. I recently covered the QuadCore mod for ancient thinkpads and the firmware replacement that entails: https://youtu.be/Fs4GjDiOie8 I received multiple requests on Details and Walking through individuals performing similar upgrades from Latin America. To me, the spirit for reviving trash grade tech to our modern sensibilities is alive and well.
Going off how people treat cars, the majority would do this the practice is ever allowed on a wide scale (to facilitate commercial services that assist them for a small fee).
The issue is that most phone manufacturers don't allow owners to do this, and most that do, do pull shenanigans that make it unpredictable and difficult.
Poorer people would absolutely choose to pay 25 dollars to extend their phone's life (replace battery + reflash to a supported firmware/os) vs buying another 200 dollar phone.
I'm hoping the EU (and the rest of the world) steps up and does what the US should have done a long while ago.
There is a lot that can be done and there is a lot that people do.