For what it's worth there's reasonably active [1] work on implementing opt-in guaranteed tail calls - but it's not particularly fast going. LLVM (the backend rust uses) needs better support for musttail (e.g. some architectures just don't support it [2]).

[1] https://github.com/rust-lang/rust/issues/112788

[2] https://github.com/rust-lang/rust/issues/153827

By-default guaranteed tail calls really isn't rust's style, because it means subtle changes (introducing a destructor, re-ordering code, etc) can change semantics without you realizing it. If you want to guarantee that a call can't allocate a new stack frame you should have to say it.

Do any widely used languages guarantee tail call optimization? It's a pretty niche feature.