I don't know, there's quite a bit of sharing, I think a large part is that bringing in a third party library tends to be a total pain, which silos code quite a bit. In my experience, excluding header-only libraries, you usually end up spending about half a day screwing with the build system to get a library entirely integrated if your build system is moderately complex (and it will be if you're cross platform). Most of it just has to do with the design of the language(s) -- linking is very complicated, there's a lack of a good module system, conventions range wildly, compiler support for modern things tends to be uneven, etc.

I think something that might make this project a bit more interesting would be an integration with CMake, which is becoming pretty ubiquitous.