That sounds like a strawman. You're ignoring maintenance and adding features to old codebases. It's usually the majority of the work done. Sure, you don't need to recode BLAS as it's doing its job. But not everything is BLAS.
! MARK 1 RELEASE. NAG COPYRIGHT 1971.
It has been revised since then to use free form, structured programming, MODULEs, KINDs, INTENTs and IMPLICIT NONE.
If we can do it, everybody can. I have already mentioned some reasons that people don't do it. None of the reasons I have heard are "Fortran is too old and clunky".