I don’t see how the langage in which is developed a software is a reason to use it or not.
It’s not like you can’t install your good-old-C++Rust-javascript Firefox browser.
It’s not like you can’t install your good-old-C++Rust-javascript Firefox browser.
Default apps are mostly good. Music is the only one I don't like in general, and while Epiphany is not my preferred browser, it seems perfectly capable (hell, it even syncs with Firefox Sync). The rest of the apps feel very pleasant to use and I never had to bother with looking for an alternative.
Using a certain operating system comes with the implicit assumption that I'm also gonna write programs for said operating system. And I'm not gonna learn some obscure version of C#/Java for that, just because the gnome project felt that they had to n.i.h. an entire programming language.
This isn't what happened. When Vala came out (2006), it was at the time the only programming language advertising such high-level concepts as found in C# (like async/await) while guaranteeing you native performance without a VM. At the time it was billed as a better C++ and a faster C#. When the elementary project adopted Vala (2007), Swift and Rust weren't things, and they would remain unstable for at least the next decade.
Today the world has changed, and while I'd argue that Rust is one of the best languages invented, Vala still has some things over it: easier to learn, binds well with C and a million other languages, faster compilation and a simpler toolchain, has built-in type annotations for Gtk and DBus, all while guaranteeing you native performance.
At some point you gotta pick the hill you're gonna die on, and that shouldn't be dev mind-share.
The horse they bet on didn't make it, why fall into the sunken cost trap, either bet on a different horse (rust), or pick a tried and true one (C) and write a decent FFI for alternative languages.
Now is there more to improve? Absolutely. Despite its use by users, development of the language itself suffers from chronic underinvestment. But I think that's changing a bit recently. (Full disclosure: I'm involved in developing the language and tooling. We could always use more contributors.)