Last time it was brought up, there appeared to be some lingering confusion and issues with how the compiler and runtime was and is licensed.
The latest version of Ada is available for a (large) fee from Adacore and for free under the GPL. There is also a version published as part of gcc, that trails the upstream version a little in terms of features -- but like the rest of gcc, the relevant parts are under LGPL, so not all binaries distributed to third parties need be distributed under the GPL, but can be under any licence one choose[1] -- without the need for a commercial licence from Adacore.
It would appear the lack of an up-to-date, gratis, version of Ada was a real problem for adoption at some point -- and the impression of Ada being difficult to get access to outside of large contractors put a damper on its popularity (justified or not).
[1] The "problem" with a compiler under GPL is that most compilers will have some kind of library code or language runtime that needs to be distributed with resulting binaries, thus forcing all projects to adopt GPL, rather than just the projects that build directly on the compiler.
More than price, what really hindered Ada was lack of adoption by popular OS vendors and hardware requirements for the early compilers.
Back in the day everyone was paying for compilers, the prices were the normal ones for the target audience.
Rational Software first product was an advanced Ada Machine, providing an early 80's InteliJ experience. Which followed the same fate as all special purpose computers.
UNIX, mainframe and other enterprise OS vendors that eventually provided an Ada compiler, treated it as second class citizen in regard to their main systems programming language.
Home computers lacked the required hardware to implement a proprer Ada compiler.
A systems programming language really needs to be "the language" an OS vendor SDK requires, otherwise it becomes just another application language that can also go low level.
Besides Ada Core, there are a few embedded and real time OS vendors providing Ada compilers.
Both, from the Spectrum days up to the time we could get them to run on 32 bits.
On those days I and many older than me were still writing business applications in Assembly. Compilers for higher level languages were constrained in what they could achieve in the amount of memory that was available.
And Ada did required lots of it. Funny enough I would bet modern Ada compilers are less resource intensive than C++ ones.