Anyone know why they are still on such an old version? The latest version is 16.1.
[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.
gcc15-15.2.0nb1 - The GNU Compiler Collection (GCC) - 15.0 Release Series
As others said, I think it has to do with all the platforms NetBSD supports.