This isn't true. Openblas and MKL are both C/C++ with assembly hardcoded microkernels. SciPy is in the process of removing the last of their Fortran because no one wants to maintain it, and newer methods in other languages are faster. Fortran hasn't been in the core of everything for decades.
Julia is starting to pick up steam here. It's a lot easier to write mixed precision algorithms in since the type system is pretty much designed for efficiently writing generic algorithms (and it doesn't hurt that Julia's ODE solvers are SOTA)