Widely adopted source code manager requires a widely adopted build system. CMake is certainly a contender but the ecosystem is too fragmented even then & you have to do a lot to try to link disparate build systems together. Also C++ is a transitive dependency hell nightmare & any attempt to solve that (like Rust has) would break every ABI out there. Given how bumpy such breakages have been in the past, I don't think there's any compiler maintainer eager for it (even MSVC has decided to largely ossify their STL runtime ABI).

Conan is certainly a laudable attempt at something like this. Without access to their metrics though, it's hard to tell if they're continuing to gain meaningful traction or if their growth curve has plateaued. It's certainly not in use in any project at medium to bigger size companies I've worked at. By comparison, Cocoapods was pretty successful in the iOS ecosystem precisely because Xcode was the de facto build/project system.