I can’t say why other people don’t use collections directly, but I think I’ve already mentioned this several times in other places: For “security” (compliance) reasons, our control nodes can’t download collections directly from the internet / galaxy. We need something in between like Sonatype Nexus or similar that works as a caching proxy or so where we can run security and (license) compliance checks centrally. We have a solution that’s accepted by our IT security for PyPI, but not for galaxy.
As @felixfontein said in another context:
Different problem, but this would help us to move away from the community package.