All good stuff I've ever heard about Fortran could be summed up as "it's easier to write optimizing compilers for it", which was probably a claim made more than ten years ago based on an interview with someone who worked for IBM over twenty years ago on Fortran compiler.

Suppose this was the only really good thing going on for it... well, this wouldn't attract a lot of people. Also, I'm not sure Fortran can boast to be the easiest language for optimization. I believe the statement was made in the context of comparing it to C, in which case, it's not such a high bar.

I've been out of grad school for a bit now, but 10 years ago is about right. There were a lot of things being published about compilers that might have well been direct ports of papers written in the 70s, "now for JITs." And honestly, if you read some of those papers from the 70s about automatic parallelization and such, it was pretty freakin' cool. And there were memory guarantees in Fortran that were not present in C that made it non-applicable. Java had most/all of those guarantees, which is what I think brought about their revival. That's probably not the whole explanation, as I'm not sure why it took Java so long (these were 2010+ papers, 15+ years after Java came out).

The very first optimizing compiler was written in Fortran, to compile Fortran. I think this was the 60s.

The use of pointers in a language vastly complicates the task of optimization. From Fran Allen, a compiler researcher and co-inventor of SSA,

By 1960, we had a long list of amazing languages: Lisp, APL, Fortran, COBOL, Algol 60. These are higher-level than C. We have seriously regressed, since C developed. C has destroyed our ability to advance the state of the art in automatic optimization, automatic parallelization, automatic mapping of a high-level language to the machine. This is one of the reasons compilers are basically not taught much anymore in the colleges and universities.