Why ferries can fill up with reservations (leaving you to wait multiple sailings)

How is it that you can show up to the ferry terminal, not see many cars, but still have to wait multiple sailings? We hear how (and why) B.C. Ferries is allotting more and more space for drivers with reservations. Plus: why isn’t there a buffet on ferries anymore? And what’s replacing it? And a few other ferry-related tidbits.