I dont understand how ex-Nokia devs could have built a phone like the N900 and then just walked away from it for 15 years
Don't forget that SailfishOS is ultimately Linux (and not like Android) - it even comes with the zypper package manager that lets you install apps and update the OS using the terminal. Part of the fun of using SailfishOS is doing familiar Linux systems managements and general operations the terminal, which any Linux nerd would love. And Linux nerds make up a huge userbase of this OS.
I mean, look at the link OP pasted, they're straight up calling it a "Linux phone", it's clear who their audience is. And don't tell me majority of Linux users would NOT prefer to have a keyboard.
It's clear that "Linux" is a big selling factor for this given that they mentioned it so many times, but they do little to elaborate on it.
It's clear who their audience is.