There are a multitude of reasons.
Firstly, I don't really have much interest in this project; I don't use Linux, (and most likely won't for a while) so I don't really have a point to update this project.
Twig doesn't really want to be affiliated with this project due to the actions of Jetray (who made the original Filtering Disabled launcher).
Bad code: The code used shell scripts as they were fast to write up, but were never scalable and never really meant to last, but the code was never rewritten to make the project better. Many things didn't work either, such as strange issues with versions, and TLS/SSL issues preventing 2022M Studio (and possibly 2014 CoreScripts) from working.
As far as I know, the only real other alternative for Linux is Windows81's Roblox Freedom Distribution.
It's made by a developer who is much more competent than us, and actually wants to work on the project.
If you want the old source, you can clone the repo and revert to an older commit.
git clone https://github.com/Vector4-new/RobloxFDLauncherLinux
git reset --hard 1d6a365037558bfb1ac3fad5498d960225161304