Yes, it's true that you can do arenas in Rust, but they are harder to use in Rust, due to borrow-checking. For example you can't store arena in a struct without lifetime.

So in a language which actively makes your life miserable in the name of safety, you will likely just use Vec<T> because it's easy. Hence, back to the previous point - Vec<T> is slow -> your code is slow and it's not even obvious why because everybody does that so it looks like you're doing it right.