Open-source + built in a slightly interesting language are the only reasons we'd be discussing an MMORPG.
Good luck to the team. MMORPG that anyone wants to play is probably the hardest challenge in gamedev and game design.
And everyone who plays large modpacks, goes around large buildings, or just sets off a ton of TNT has seen how it has suffered for it.
On the other side, anyone who has seen the selection of mods available for Java edition vs bedrock edition (the C++ rewrite) despite a modding API for bedrock being officially supported has seen how it has benefitted from this.
What does that have to do with the parent comment? The usual argument I've seen is that game developers "move too fast", "don't have everything designed ahead of time", "have to iterate quickly" and Rust's insistence on writing correct code gets in the way of that during the prototype phase.
Java doesn't really have that issue as it is quite a bit more forgiving than C++ and will happily let you hammer a square peg into a round hole at the expense of performance, as evidenced by Minecraft.
Did not know that