downloading a random binary that creates random files in ~ is pretty 1990's
The idea may be old, and yet the execution is definitely modern!
itch-setup is not a self-extracting file, it validates the version folder, comparing it against a signature, healing files that are missing.
For initial install, all files are missing, so it extracts them all (it does so without storing the archive itself on disk - extraction is done on-the-fly, while it's being downloaded). For corrupted installations, it just repairs the files that need to be repaired. For upgrades, it applies optimized patches (the same software is used both for installation and updates).
Also, it's all open-source (see Github repo), and the same codebase runs on Windows, Linux, and macOS - except for the interface, which is native to each OS, of course. On top of that, it allows the app to self-update seamlessly on all three platforms.
I've wrestled with distro-specific packages (and even new, "self-contained", "sandboxed" formats like AppImage, Flatpak, Snap) before, but at that time we don't have the resources to support it. Investing a few months of part-time work on our own unified setup solution is already a small miracle in itself :)
If we end up shipping a Flatpak or Snap, it'll be for itch-setup, which will in turn install the itch app. It's not in my TODO list for the immediate future though!