The reason for this is that on my system, the static or delay loaded method always picks the (obsolete) system-installed OpenAL version (needed for some old games) which is not wanted here if there's another one in the local ZDoom directory.
This also removes the dependency on the broken import library that comes with OpenAL Soft which causes compile errors with more modern MSVC compilers on default settings.
Christoph Oelckers