Game contribution rate is the biggie for large turnover requirements, and an often overlooked factor in why players don't ever see winnings from bonuses.
If you have a big wagering requirement, games that only put 10% of the stake towards completion just make it take forever to complete. Obvious, but online casinos anticipate a lot of players not reading the fine print on their bonus, so they just play whatever games they like without considering the game contribution rate, or game exclusions.
