In addition, OpenRepos hosts more than just SailfishOS applications (e.g. Meego/Harmattan).
Also, Chum depends on Jolla infrastructure (OBS) while OpenRepos is hosted independently. The future of OBS has always been unclear, and while it seems we are going to have it for a while, there has been no commitment from Jolla to keep it available.
But regarding the original question, there was an effort to do exactly that but it is stalling at the moment.