Language choice is secondary to methodology, but Ada does a darn fine job of checking an awful lot of methodologically useful things up front.
It's less the language than the ecosystem and the infrastructure. It's eminently possible to develop 'C' that's exhaustively tested - I've done it. I am not sure that is true of C++ or Java.
Fine, I'll grant you Ada, and it does seem like a good language for these kinds of things. But you have to acknowledge it's not going to become a popular language for regular software projects.
Chances are, when you travel by train or take a plane, the control system was developed in Ada.
When human lives are at risk, C is becoming less and less an option.
And when the company still goes C, many countries have certifications in place like MISRA, that make C look like Ada with C syntax.