I'm not going to jump the "Fortran is dead" bandwagon as it is a language that continues to get used in simulation code and I feel it's never really going to be replaced. As you mentioned it has good properties for writing that kind of code, good compilers, etc.

That said, it is a very niche language, used mostly in the physics simulation & supercomputing world. And idk how popular NN are in that sector, but it seems to me it's a niche inside a niche... So you will need to dig a bit to get answers. Maybe the people at r/Fortran will know more.