DA Canon has F/M and F/M, or maybe just one big F/M pairing. If someone ships M/M, but doesn't want to make the female characters into harpies or kill them off, they may add the F/F ship in the background as bit players and make some noises about them being ~so important~.

/has a couple fandoms that have followed this pattern. It makes it really hard to search for your F/F ship, because everything with them is also tagged with M/M, and a small percentage of those will actually focus on your F/F ship, but if you screen out the M/M ship, you'll miss them