Only once has that happened to me. On that ride, very few people did the full 100-mile route, which I did in respectable time. But when I arrived back at the HQ, the lot was empy, vendor tents were pulled up, and the building was closed. No shower for you!!! I guess they figured the century riders could finish in 3 hours just like the 30-mile riders. Anyway, I never went back.
Find the ride's web site and give them some feedback. Rides usually have a cut-off time; but a century should generally allow at least 7-8 hours before they pull the plug on support. And running out of the pre-purchased food is just inexcusable.