In part it's a cultural thing. Ada is considered "complex and verbose" (but compare with Java). Ada is, of course, from the DoD, so it's "obviously bad." Most importantly, Ada requires a bit more thought before you jump into the code.
The interesting thing about Ada is that a skilled practitioner learns how to use the language to his advantage. You code so the compiler checks as much as it can, so you can concentrate on things the compiler can't check. When the compiler and you agree the code is correct, it probably is, at least with respect to typos and coding errors.
One big criticism I have with most languages, even those with a type system, is they don't support strongly typed scalars. But that's where type errors are most common. I don't think I ever tried to "add apples to oranges". But I have tried to add "count of apples" to "count of oranges" (or more specifically, once tried to add horizontal pixel location to vertical pixel location.)
Furthermore, those who think their C code is "close to the machine" don't know much about modern machine architectures. Compilers do a LOT MORE work than they did in the days of the PDP-8/PDP-11 or original x86 family. Ada (among other 'higher level' languages) provides the modern compiler with a lot more information for code selection and optimization. For example, register flushing is a lot easier to manage in Ada because pointer types are always declared as such, and unless there are specific language constructs, the compiler can prove a given variable will not be accessed through its address (and therefore doesn't have to spill the register to memory.) That's a simple example, compiler optimizations and instruction scheduling are very complex topics.
Finally, I've always thought C syntax was harmful, because it's so easy to make a mistake, either through ignorance or simple typo ("=" vs "==").
I know experts can do amazing things in C. Aren't that may experts out there slinging code, and most of the software we use these days shows it!!