Ada and D are also in the process of adding memory safety to the base language too.
The actual question is why nobody cared that much until now to put it in mainstream languages. The answer is, as you know, browsers.
Not giving any concrete examples is just proving my point.
Which C variations are both thread and memory safe? Which Ada variations are both thread and memory safe ?
AFAIK, such variations do not exists, and people claiming that they do on the internet and then failing to provide a simple link when requested multiple times by others to do so just seems to confirm that.
So anyway, what subset of C allows the use of dynamic heap memory allocation and enforces safety?
That's true, and I know you are not claiming this, but MISRA C is neither memory nor thread safe, which is what we are talking about here.
Writing MISRA C code with data-races is trivial, and no "linter" for it finds those.