I actually see Ada/SPARK referenced pretty frequently in discussion with other Rust programmers, and I've been to at least one Rust talk in which learning from Ada was the main topic.

Anyway, it's hard to blame people for looking elsewhere when the best Ada compilers were proprietary for so long.

I not so much, beyond some occasional assertions of Rust being responsible for features that Ada already had them first.

As for compilers being expensive, while true, I learned Ada via books a couple of years before being able to put my hands on a compiler.

Then again, maybe that is no longer fashionable way of learning.

Ada seems very nice, but compared to rust I think it lacks momentum and (some) ergonomics. It's sad, but a C-like syntax on top of the Ada semantics would possibly be more popular.