Option to enable Shared libraries build

I have created the AUR package `filament` (https://aur.archlinux.org/packages/filament/) in order to make access to the library for Arch users.

Since it makes more sense to have shared libraries for a distribution package, I would like to use CMake option `BUILD_SHARED_LIBS` to build shared libraries.

I'm wondering if there is a reason why all libraries are explicitly forced to static build?
Without `STATIC` keyword in `add_library`, CMake is building static library anyway.