Mlua works for many use cases but is a wrapper around the C code, so you need to bundle C as part of the build. So this is worse for cross compilation and makes it so you can't easily use mlua projects in wasm32-unkown-unknown. An example is that it would be hard to run a game in the browser that exposes Lua scripting with mlua.

The other reason is that because mlua is just a wrapper around the C code, it has unsafe you can't really get around. So for example Lua is used in Redis, which has this critical CVE https://github.com/redis/redis/security/advisories/GHSA-4789... that a memory safe version of Lua wouldn't have to deal with.

Mlua is still fine or even better for many other cases though!