I work for a corporate events company (although I don't think I'll be going back) Anyway, they do things I really do not agree with. For instance they were catering for a wedding. The bride and groom paid for a bottle of red wine, white wine and bottled water on each table. When the tables were cleared they re bottled the wine and sold it back to the guests, including the bride..!!!!
At a 3 day cricket event they also did the same and put the previous days bottles, refilled, back on the the tables. The same with the water.
The reason it gets left is so much happens at the meal. Champagne gets handed round for the toasts and as soon as the meal has ended the room has to be cleared really quickly to get ready for the evening do.
As quickly as possible before they finish the wine....!!!!