I am not sure what to do about the burnout problem. The way he described it is very on point though. Since everyone working on the project is overloaded there is a great feeling of things only get done if you do them.
Most of my open source work was in the pre-GitHub days when we used mailing lists, not pull requests, to build community. I do think there was something better about that for the project itself as it encouraged a lot more discussion and community building. PR's and Issues become silos and are not great for general discussion. I think they also encourage drive-by contributions which honestly are intoxicating initially but once you see people are not coming back become defeating.
I'm not sure whether it's more to do with the way the project is organised, the state of the codebase, or the sort of person that's attracted to working on Rust in the first place.
What's that even supposed to hint at?
Rust has something of a self-image of always being best-of-breed in everything it attempts, so I could believe that it might be particularly attractive to those sorts.
Other possibilities might be that Rust developers skew younger than average (I don't know whether that's true), or that its six-week release cycle attracts people who think that a year is a long time.