Expectation mismatch

Yeah, but it's not a pmOS-specific phenomenon. That's exactly what was happening some ~15 years ago when SHR (a distro with Openmoko roots) was being ported to other devices, such as HTC Dream or Google Nexus - and once the ports started to form some shape, there wasn't really an audience anymore as people have already moved to the next generations of phones.

That said, there is a handful of devices that have a chance to actually become daily-driveable smartphones for some people. Still, arguably the best supported one had most of the work on it done by its vendor (Librem 5) - supporting a device well is a full-time job for a team of diverse people for a good while, especially when you can't stand on a giant's shoulders and have to do plenty of groundwork by yourself.

Meanwhile, a hundreds of devices can boot into a reasonable userspace and maybe not exactly be a phone, but provide a chance to perform some playful cleverness to technologically curious people. This has tremendous value too.