You mean in the language itself or its applications. Honestly I’ve heard about a lot of really cool things written in Fortran. Honestly, I wouldn’t mind learning it, but I’m far from a “ top-rate computer scientist” so no Ike using Fortran would be interested in me.
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.
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.
Enough of good programmers choose unpopular languages, and for different reasons. Some genuinely find particular aspects of the chosen language appealing, and since they are in general good programmers they don't have a fear of unemployment or the pressure to build their career -- they've already established themselves in their field and don't need to reassert their skills and knowledge.
Others may opportunistically choose a new, but still unpopular technology, sometimes because other good programmers seem to have chosen it, other times because they may hope to gain more popularity / acclaim, which is easier to do in a new, and especially in a small field.
Furthermore, it just so happened that popular technologies in the industry today are all kinds of bad. Just of sheer desperation / disdain to a particular group of related technologies one may want to try to switch to a niche technology that seems to go against the mainstream.
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However, in all those cases, there must be something "interesting" going on for the technology in question. I don't know enough of Fortran to claim there's nothing "interesting" going on for it, but it's possible that there isn't. In which case, there won't be an incentive for good programmers to choose it over similar technology that has that glimmer of hope that it's going to be so much better.