It sounded like the original promotion with just fights inside Europe went well. It was the expansion of the promotion to include the USA that seemed to have caused the problem.

I suspect "well" might be an exaggeration. I bet they were doing the same complex-claims-process, but no consumer action groups got involved.

Without a consumer action group, most customers will just be disappointed when told that they were disqualified because they filled the form in in black ink instead of blue. The few customers that make a big fuss can be given flights.

It's only when a group gets involved that you have to give them all what they're entitled to, and it gets expensive.

I think the bigger difference is that initially the sort of person that used the promotion was somebody who saw it as a reason to pick Hoover over Zanussi or Electrolux products and often bought the higher end washing machine or fridge they were actually looking for rather than the cheapest vacuum cleaner, so Hoover often did better than break even on the promotion when taking into account their profit margins versus whatever wholesale price they got on the flight tickets. And lots of genuine customers didn't bother filling out forms, and few people looking to buy flight tickets to Italy for about £119 decided to get a vacuum cleaner and some booking hoops to jump through instead...

When £600-£1000 face value tickets were offered, the logic of buying the lowest cost qualifying electrical product instead of the flight to the US started looking entirely different...