(1) Compatibility with legacy FORTRAN. Although it's not difficult to work with legacy FORTRAN via C, it's seamless to pass data around between legacy FORTRAN and Modern Fortran.
(2) The mathematical and array syntax. It's tough to beat Fortran's mathematical notation and easy use of multidimensional arrays.
This. As someone who once did a lot of computer graphics programming in C (not C++), I would have killed for proper arrays. Modern C, with variable length arrays, helps, but still...
A long time ago, at a university far, far away, I worked with SGI's gl library, which had FORTRAN bindings. In retrospect, that seems like a very smart idea. At the time, we stuck with the C bindings.
(1) Compatibility with legacy FORTRAN. Although it's not difficult to work with legacy FORTRAN via C, it's seamless to pass data around between legacy FORTRAN and Modern Fortran.
(2) The mathematical and array syntax. It's tough to beat Fortran's mathematical notation and easy use of multidimensional arrays.