Not all linux systems are running a desktop GUI, for example…most servers. /edit to add or expand/ I use Etcher on my laptop but I use the command line with my server in the closet…plug in the USB, go back to my laptop and do everything remotely.
Also, as a linux user/admin for 25+ years I’ve seen these apps come and go. Inevitably the app gains so much popularity that the dev wants some money for it… so they add advertising to the app. Then some other app comes along to replace it, rinse and repeat indefinitely. If your shell commands are POSIX-compliant, they’ll last for decades or more.
Etcher itself has advertisements for https://www.balena.io/ products while your USB drive is being written.