Discord changed the communications of an entire generation, removed ideal low priority messaging and replaced it with a vulnerable and bloated service that now offers to sell you games and track your every move. Everything on Discord is unencrypted by design.
Rust is moving from irc to discord as a result of mozilla sunsetting their irc server. I know one datapoint is not a trend, but it's a high profile datapoint.
I can more or less easily get my data out of github (I can host a repo elsewhere, write a script to scrape the issues, etc.) I don't like using the non-git parts of it for much (ie why write a wiki when you can just make a repo full of markdown files?) Discord is a whole other level of walled garden. It's a black hole of information, and that information isn't owned by you. Discoverability is nonexistent.