Having only recently looked at Ada I don't really understand this. It does look like Ada offers a lot of really nice features that other languages haven't yet caught up to.
For example, SPARK allows formal definition of correct code behaviour within the function definition. This appears to me to mean tests are written into the function at the time you write the function. That's huge from a maintenance standpoint, and it likely provides extra information a compiler could take advantage of.
> where no errors are allowed, which could possibly lead to loss of human lives, very few care of using Ada.
Loss of life is one area, but surely anything financial would benefit from this - as well as anything dealing with personal data (e.g. identity management)?