Basically, once you have an OS level package manager, you have issues of versioning and ABI. You have people writing to the lowest common denominator - see for example being limited to the compiler and libraries available on an old Red Hat version. This need to maintain ABI compatibility has been one of the hugest issues with evolving C++.
The OS package manager ends up being a Procrustean bed forcing everything into its mold whether or not it actually fits.
Also, this doesn't even have the issue of multiple operating systems and even distros which have different package managers.
Rust and Go having their own package managers has helped greatly with real world usage and evolution.