If the generator is itself in C++, then it requires to have 2 full toolchains to bootstrap it. Then if the developer have a great idea such as "hey, I got access to all my code! Let's reuse it" then you have to build the package twice. Since everytime you do that you increase the number of packages to be built on the host toolchain, after a while they start to bleed into each other (due to buggy build systems in the dependencies) and when you execute the final binary, you get "wrong file format" errors on the target (or worst, sizeof() mismatch at runtime)...

I am not saying there is no solution to these problem, of course there is. All I said is that it makes bootstrapping a system much harder than it would otherwise have been with constexpr. Many devs avoid those issues because dependencies rarely change and once you fixed all issues, it will most likely stay stable.

Mature and "made for embedded" projects tend to be better since cross compiling have been taken into account in each steps of the pipeline. But if you start pulling random code from the internet, expect the worst.