Saves a lot of duplicative work at the projects, is easily mirrored, imported into web pages, etc.
With mentioned problems of - Google threat covered by community hosting and replication. - Separate / overlapping project / topic focus covered by a flexible tagging and views system. - Not easily being able to find and read what other projects in the space are referencing covered by now having a combined database itself. - Maintaining effort of growing multiple bib systems covered by everyone lending some minor time coding to the main bib project db itself, freeing up time for each project to then focus on submit / tag and reading / using the materials as the more beneficial result.
And so on.