As far as I can tell, what you're missing is the massive ease-of-use and approachability, especially for non-technical users, of a web-based graphical "convert X to Y" interface vs. facing command line ffmpeg, which they probably haven't heard of.
Once an app is installed locally it is more convenient to use - that is why it is so common for apps to replicate (or just wrap) websites.
If you are not interested in the self-hostable part there are lots of online converters.
Why on the front page? That question might also have a non-technical answer. What's going on in news and events? Who's been setting up file translators and then "Dude I have over 4,000 soundfiles, pictures, address-books..." ... "Whoah? Like. howdy manage that one?" ... "People just submitted it. Zuck fucks"