Maybe this is my old skool C++ bias, but every time I’ve inherited a project using CocoaPods I’ve found the code to be of poor quality and the Pods to be either corporate libraries (third-party analytics, crash logs, etc.) or wrapper code of questionable quality that hasn’t really provided any benefits over a couple of hours of writing some simpler code yourself.
And you yourself mentioned Boost, which is kind a code ecosystem of its own, all open source. But I think C++ has problems with libraries because it’s such a pain to add a library to C++. If the library is C++, you can’t ship a binary and header file like with a C library because the ABI needs to match, so you have to compile the thing. And then people like Boost do template wizardry that consumes compile time to produce magic, but some developers value the compilation speed over magic, so they don’t use anything heavily templated. But if it isn’t templated, it likely could be written in C if it isn’t a big UI framework, and be available for everyone. So, no C++ library ecosystem.