They didn't choose electron because it is light on resources. They chose it so they can have a consistent experience on many platforms. That experience may be horrible, but it's consistent. I guess that if they actually made it silicon native and you were running the hub on a top of the line hyper expensive Mac studio, the spinning Unity logo at the start might not stay enough time on your screen for you to start regretting the life choices that brought you to this moment, therefore Unity hub would not work for its intended purpose. Finally, Unreal's launcher is also super terrible (also made electron), so I'm guessing this is the one area where Unity actually chose to out-do them.