Apparently they did away with jemalloc in favor of the system allocator that same year but nonetheless when I came back to it years later I was very happy to learn of its removal.
[1]: https://github.com/rust-lang/rust/pull/55238
[2]: https://blog.rust-lang.org/2019/01/17/Rust-1.32.0/
At the time in 2018, however, I was using Linux but now use Windows. I just now learned that Rust used the system allocator in Windows longer than for Linux [2] where it was still using jemalloc for the majority of 2018.
Why?
It also does not give a good first impression at all to newcomers to see their hello world project built in release mode take up almost 2MiB of space. Today it's a much more (subjectively) tolerable 136kiB on Windows (considering that Rust std is statically linked).
Right, but, so what? I can't imagine a practical reason this matters for the vast majority of situations. So either you're doing something pretty niche, or it's a purely aesthetic complaint.
Those are certainly valid. There are entire Linux distros whose mere existence is as the answer to what is only an aesthetic complaint.
If nothing else doing otherwise is likely to cause compatibility issues for someone at some point. For example see all the problems Go had with DIY syscalls pretty much everywhere except for Linux.
There's a legitimate question of whether the kernel ABI or the libc API qualifies as the system provided facilities on a linux box. But that uncertainty only furthers my latter point about compatibility.