I don't see why. If the Steam-DRM'd version of a game requires Steam installed in order to play, they can just add the Steam package as a dependency.

Possibly a bigger issue would be that Steam has incremental updates (fixing a bug in a game requires downloading a fixed binary but not the multi-gigabyte data files) while most Linux package managers do not support incremental updates (when Debian releases a new LibreOffice package that fixes some dependencies for the s360 archictecture, I still have to download hundreds of megabytes of changes on amd64).