FORTRAN's problems with rentrancy don't mean that FORTRAN programs can't be multi-threaded, it just means that each function has to be run from the same thread every time it's called.

I'm not saying FORTRAN is great - clearly it has a bunch of problems which C mostly doesn't have, which is why people mostly use C instead. But this one single advantage (allowing the compiler to do optimizations on array work) is so important to some people that it will always be around.