While not strictly related to gfortran, Agner Fog has written a perspective on contemporary C++ compilers:
The number of C++ compilers on the market is decreasing. Many compilers have disappeared from the market or are no longer maintained. Do you remember compiler names like Borland, Embarcadero, CodeGear, PathScale, PGI, Zortech, Symantec, Digital Mars, Watcom, Codeplay, Glockenspiel? It is becoming increasingly expensive to develop C++ compilers because the x86 instruction set now has around two thousand different instructions and the number keeps growing. At the same time, the C++ language keeps developing with new complicated features being added steadily. Optimization techniques are also becoming more and more advanced, where different compilers compete to produce the most optimized code.
More in the full article titled “Which C++ compiler is the best?”.
The situation is mirrored to an extent in Fortran where both Absoft and Lahey have shut down recently. (Although it could be completely different reasons.)