It’s in the post. They wanted immutability:

“Unraid has always been a so-called immutable OS— however you modify your server, if you go in there, you type the wrong command, you delete all the files from your root, you still could just reboot and you’re back to the virgin release… and that’s a big reason why we’ve chosen Fedora [uCore].”

— Tom Mortensen, creator of Unraid