It's easy to get lost in the modern way we look at compilers and toolchains, but it wasn't always like this. Free compilers basically didn't exist 30+ years ago. Certainly none of the free compilers were good. For the longest time, your only options for Ada compilers were priced at government contractor-levels (think $10k per seat... in the 80s). It's also an extremely complicated language, while C isn't. A single, moderately skilled programmer who can at least make their own FSM parser can write a reasonably complete C compiler in the space of a month. There's no hand-rolling your own Ada compiler. Even just complying with SPARK is a herculean task for a team of experts.

This is much the same reason I'm highly skeptical of Rust as a replacement systems language to C. A multitude of very talented folk have been working on writing a second Rust compiler for years at this point. The simplicity and ease of bootstrapping C on any platform, without any special domain skills, was what made it absolutely killer. The LLVM promise of being easily ported just doesn't hold true. Making an LLVM backend is outrageously complicated in comparison to a rigid, non-optimizing C compiler, and it requires deep knowledge of how LLVM works in the first place.