Film is unforgiving in exactly the conditions a wedding reception provides. Dim rooms, moving people and a fixed flash produce a lot of frames that are dark, blurred, or a bright face against a black room. You do not find out which until long after the day.
Then there is the collection problem. Cameras end up in bags, on the wrong table, in a car, or at someone’s house for a fortnight. Whatever comes back has to be developed and scanned before you see a single image, and every roll costs the same to develop whether the shots are good or not.
And a disposable camera records one kind of thing. No video of the speech, no voice of the grandparent who spoke, nothing that moves or makes a sound.