“I’m sure the moisture and Sea air took a toll on the old wooden support structure of that Deck.
“
Likely poor bracketry and fastener deployment/selection too.
Those Houses have been there for years.
The outside shot of that Deck before the collapse make it look like it was original the House. The exterior upkeep for that House was lacking.
That Deck should have been able to support much more weight than those 15 Partygoers.
Mike Holmes would have had a field day with this.