There is no rule that donors need to donate to multiple projects. Donors can give to whichever projects they want.
COCM distributes the matching pool according to the preferences of the whole community of donors. It rewards projects with diverse bases of support and is much harder to game than regular QF, which can turn into a popularity contest won by whoever rallies the most people to give only to them.
COCM has been Giveth’s matching mechanism for over two years, including last year’s Stellar round: Cluster Match QF Announcement. It works the same way for every project, and we share how it works so everyone can understand their results: https://wtfiscocm.streamlit.app/
We’re sorry the outcome wasn’t what you hoped for this round.