This was because Skype’s file transfer was Peer-to-peer, so it wasn’t Skype itself hosting the files. While discord is actually hosting the files, which is much more costly.
But discord supports sending messages to people who are offline. It kind of breaks the paradigm if certain features require full synchronous communication. Maybe supporting p2p transfers during a video / voice chat would work though.
Actually yeah. It feels like voice / videos were kind of tacked on. There isn't a really good web based chat tool that doesn't require some sign in and configuration. File transfer isn't like that and people can easily drop links to third party services in any chat.