Having worked on writing DB internals in both Rust and in other languages, I can say that there's huge time-saving advantages to having something higher-level & garbage collected at the layer of the query parser/analyzer/compiler. The borrowing/ownership semantics can get really snaky when dealing with complicated expression trees, iteration patterns, etc.

(And while Rust's enum-based algebraic types & pattern matching are nice, they're actually fairly limited when compared to what you can find in e.g. Scala or F#, Haskell, etc.)