One thing that's noticeable is most of those projects are Linux-only and many of them are around GNOME / GTK ecosystem. Most of those projects have no Windows

One thing that's noticeable is most of those projects are Linux-only and many of them are around GNOME / GTK ecosystem. Most of those projects have no Windows versions. The ones that have them have really bad compatibility with it (e.g. GIMP, GTK3). Meson has a preference of simpler code bases leaning more on the C-heavy side. That's usually not the case with big, old and commercial C++ code bases. The programs that need complex build systems that require things like compiling a code generator first and then compiling the rest of the project with the generator etc. are quite common in C++ world to tame the language's shortcomings. Libraries like Qt, Protobuf and GRPC often introduce a crazy amount of build complexity. CMake's complexity is directly result of that and it is currently the only build generator that can cope with that using basically every compiler in existence (including proprietary ones like ARMCC, ICC, MSVC and very limited ones like SDCC). Even Bazel cannot handle the same number of compilers and feature sets. That's the thing that makes CMake gold standard not its string-driven scripting language. CMake shares quite a bit history with C++ and you hear sentences like "it's the only thing that works for this level of complexity" for both.