Promoting their bonus will not be classed as offering an incentive; neither should any game strategies.
Typically, affiliates have been offering some sort of money or item to depositing players which they would pay for out of their commission. In some cases the value of the incentive would be higher than the affiliate requirements, e.g. minimum deposit and so the player would be guaranteed to make money as would the affiliate. 888 on the other hand would be guaranteed to lose money as these sort of players would not come back to play in the future.
So you can see why 888 are not to keen on affiliates offering incentives. Players who use incentives are generally not players 888 wants to see.