One big reason Nim never really caught on is because we’ve got lots of fast-ish languages with garbage collection (like Go, which sucks a lot of oxygen away from Nim IMO). Rust introduced a new concept to the mainstream that lets you program safely without a runtime hit for garbage collection.
To my knowledge, Ada doesn’t have an equivalent to Rust’s borrow checker. I also think I covered that base by specifying “mainstream” 😀