speaking personally, its rather a shame no project actually took creating
a Linux phone seriously enough to be a solid player.
Might have been a terrific way to expand Linux to end users who wanted more
choices, but who would not know about Linux otherwise.
Kare
One the main issues with Linux on phones is that of hardware. It changes often because users want the latest and greatest, lots of the hw users proprietary drivers and/or binary blobs that are basically black boxes. There have been efforts to take the kernels from Android devices and use them to boot into a more traditional UI like KDE plasma, but what trends to happen is that the devs learn just how optimized the various drivers are and how difficult to access them with standard non Android Linux apps and tools.
I followed the pinephone and librem 5 camera work closely for around 18 months and it was astounding how good the camera is on paper (specs) vs how badly it performs with an open source driver. And that's just one piece of the ecosystem.
As pointed out, apps and easy access to them are what make or break a device, and currently most apps are fairly iOS/Android specific, so porting them is difficult and companies just don't see the value in offering them for a 3rd platform.
The OpenMoko FreeRunner beat the iPhone to market, iirc, or was at least contemporary, but iOS got their app store up and were able to capitalize on their name and brand reputation, whereas the FR was basically an enthusiast phone.