So few people trained or specialized in language implementation and compiler writing actually get the chance to write compilers. Those jobs are just so rare that many people in that area re-specialize into something else (like AI these days).
The GNU gcc groups win is rarely considered these days, but kids who were stuck with masm, risc asm, or Basic thought they were heroes to the hobby.
Slowly, the FOSS compilers grew in features, and commercial entities realized it was less risky to embrace an established compiler ecosystem, and paid people to port in an experienced user-base.
Starting from scratch is hard, as people often make the same logical mistakes. =3
"There are two mistakes one can make along the road to truth...not going all the way, and not starting."(Prince Gautama Siddhartha)
Then there are the people building compilers accidentally, like in the <xyz>-as-code space. Infrastructure automation deal with grammars, symbol tables, (hopefully) module systems, IRs, and so forth. Only the output is very different.
And of course the toolchain space is larger than just compilers. Someone needs to maintain the assemblers, linkers, debuggers, core runtime libraries. If you are building a Linux distribution, someone has to figure out how the low-level pieces fit together. It's not strictly a compiler engineering role, but it's quite close. Pure compiler engineering roles (such as maintaining a specific register allocator) might be quite rare.
It's a small field, but probably not that obscure. Despite the efficiency gains from open-source compilers, I don't think it's shrinking.