I've both worked in HPC and written Fortran. C++ is almost always preferable because Fortran is too limited as a language outside of numerical code. Most HPC stopped being limited by the performance of numerical code 20 years ago. Instead, HPC codes were and are commonly limited by memory bandwidth and locality, two things C++ is almost uniquely suited for.

The kind of C++ written for HPC tends to be much simpler than the kind of C++ used to write e.g. database engines. The complexity of C++ is not that onerous in context and Fortran isn't exactly an exemplar of ease of use.