XAR development began in 2014 and hit production use in an early form in 2015; this was before some other options were out there, or before, I believe, AppImage went the squashfuse route.
XAR doesn't aim to, say, represent a sandboxed filesystem or provide some isolation or provide a specification for GUI apps to seamlessly integrate with your desktop. Instead, the main idea is to just get a single file that, when run, mounts a filesystem and runs a command inside it. In my mind, at least, it's a simpler, smaller primitive you could build other systems on top of (like we have with deploying Python, Lua, and Node).
XAR doesn't aim to, say, represent a sandboxed filesystem or provide some isolation or provide a specification for GUI apps to seamlessly integrate with your desktop. Instead, the main idea is to just get a single file that, when run, mounts a filesystem and runs a command inside it. In my mind, at least, it's a simpler, smaller primitive you could build other systems on top of (like we have with deploying Python, Lua, and Node).