I have a feeling there are plenty of excellent NIFs for most situations so most people using Elixir haven't been very dependent on Rust optimizations. Especially the web people who usually don't need that level of optimization, unless you're a giant like Discord, which is relatively unique.

Although I wouldn't be surprised to see more and more of Rustler as both Elixir and Rust gain in popularity. There's probably plenty of low-hanging performance fruit for any future rustler devs.