Somebody set up the chairs before the event started. Someone always does the job that nobody claps for.

Everything that runs smoothly was arranged by somebody before anyone arrived, which is precisely why you did not see it happen. Invisible work stays invisible because it worked. The people doing it are usually not waiting for thanks, and that is exactly why noticing them counts for something.

Find whoever did the setup at the next thing you go to and say something to them directly. Then take a turn at that job yourself, including the part where nobody notices. It changes how you see every smooth-running room you walk into afterwards.