I'm guessing the gigantic size is due to it bundling Chromium as it's an Electron app. I've been wondering why we still haven't fixed that problem with some form of compression (although I wonder how feasible that would be with binaries). Signal takes up 400MB, Element takes up 300MB. It just feels like way too much.
Especially for an app like Etcher, which I'm guessing most people set-and-forget until they need it. Most people aren't constantly burning ISO's onto USB's.