The big thing I always see is that it has a few important limitations, and those limitations mean that extra optimizations can be used.

https://stackoverflow.com/a/146186

> What exactly is it about Fortran that makes it better for an HPC env and numeric computing than c++?

Fortran is an easy language to learn. A domain expert doesn't need to spend months or years to learn C++, they can write safe and performant Fortran code in almost no time.

Apart from string processing and a few other warts, Fortran is surprisingly similar to working with Numpy - avoiding explicit loops and doing operations on arrays, slicing notation, etc. It can make a lot of computational code really easy to write and easy to read, thus easy to understand and get right.

Which makes sense when you recall ForTran = Formula Translator. It's literally designed as language where you should be able to write code that's one-to-one with your equations.