Couples never think about audio, and that is exactly the problem. Bad light is forgivable - it reads as mood. Inaudible vows are not forgivable, because the vows and the toasts are the film. Everything else is coverage.
Every ceremony gets a lavalier microphone on the officiant and on one partner, a dedicated recorder placed near the altar, and a board feed pulled from the DJ or band for the speeches. That is multiple independent sources, on purpose, because a single failed mic during the vows cannot be re-shot.
No photographer can make this claim. A missed photo can be recreated in a portrait session after the ceremony. A missed vow is gone.
