Sorry I know you are asking an honest question op but the title of thread made me burst out laughing, literally.
Unfortunately most of the trips I've been on have cost me money (e.g. cab fare to the airport at stupid o'clock in the morning or night when there's no public transport, tips for long suffering coach drivers and restaurant staff, meals, drinks, toothpaste for all the kids who forgot theirs, sanitary towels (always so many sanitary towels and we're never allowed to add them or other toiletries to our trip budgets even though we always need to buy/provide some). Yet I still go on them despite the lack of financial reward so there must be some appeal! 