Because it was a kickstarter that was run like a scam, was years late to deliver the first device, the hardware was already not good at the start due picking an automotive SOC, the form factor was bulky, and the software was really buggy.

GrapheneOS is a much more practical open source OS to use Linux on a phone.

Because it's prohibitively expensive for something that isn't guaranteed to be a usable daily-driver for most people. Also IIRC the hardware isn't quite worth the price tag in-and-of-itself.

Partly because most people don't really care if something is FSF endorsed or not. Partly because it's far from a great user experience.