The problem for older languages is that the bar for what's expected of a language has risen substantially. A long time ago, languages weren't even expected to have implementations. Today, not only are implementations expected for all major platforms, languages are also expected to run on phones and the browser, include package managers and library repositories, have a language server implementation and editing modes for all major IDEs, be open source with active development, provide extensive documentation on the scale of a book, and also promote a vibrant and active community. Oh, and to top it off, users don't want to pay for any of that. It's just expected, which is why most languages these days only come out of large tech companies that can afford to fund all of the above with no expectation of profit.
A better starting point might be http://www.GetAdaNow.com/
Accessibility is really not the problem. The problem is, Ada is an old language that has many similar problems to C: lack of a good package management story, and a design by committee making language evolution glacially slow (though that also doubles as a feature). It also lacks a vibrant ecosystem like we can find in other popular languages.
Furthermore, SPARK in particular takes the concept of safety much further than Rust or Zig do right now, as it allows proving the correctness of a program according to a formal specification. Rust/Zig only care about proving the absence of UB. This makes SPARK much more complex, and thus have a much higher barrier of entry.
[0]: https://www.gnu.org/software/gnat/
[1] https://learn.adacore.com/index.html