A counterpoint: Vala hasn't done a 1.0 release yet.
But still, back at that time (2014) there was far less research done on how Rust library authors can ergonomic bind to C/C++ libraries that have their own object system. Nowadays people have figured out some techniques and we can actually use GTK and Qt from Rust, albeit in an awkward manner (lots and lots of macros).
Vala had made up its mind for many years on what it looks like and feels like. Older Rust version had green threads and IIRC even a garbage collector, it was absolutely not the same language as Rust 1.0.
But still, back at that time (2014) there was far less research done on how Rust library authors can ergonomic bind to C/C++ libraries that have their own object system. Nowadays people have figured out some techniques and we can actually use GTK and Qt from Rust, albeit in an awkward manner (lots and lots of macros).