They are still general very easy to install. Also, C programmers don't seem to use any package managers other than the default system package manager and maybe git sub-modules (at least, not that I know of).
For what it's worth, as someone who primarily writes C, not C++, I use the system package manager, vendoring, and sometimes Git submodules, depending on the project. On Windows, when I'm using MSYS2, I use the pacman package manager. If I'm targeting MSVC, I use CMake. For CMake, on Windows, I create my own directory where I place prebuilt dependencies for CMake to find [1]. With this approach, I can rely on CMake's builtin find_package behavior (no need for vcpkg and configure-time toolchain flags).
[1] https://cmake.org/cmake/help/latest/command/find_package.htm...