It's almost certainly due to supporting platforms like VAX and other, more exotic ISAs. GCC can have weird regressions [0] in "less tested" architectures, so I presume they use a single, known good release across all platforms for consistency's sake.
[0] GCC still supports PDP-11, for example, but for a while modern GCC had some major codegen bugs. Last I checked, the maintainer had made heroic efforts to fixing the bugs, but that's just an example of where bitrot silently renders a target unusable.
[0] GCC still supports PDP-11, for example, but for a while modern GCC had some major codegen bugs. Last I checked, the maintainer had made heroic efforts to fixing the bugs, but that's just an example of where bitrot silently renders a target unusable.