I know that the fluctuations in price in terms of the economy can be annoying, but it also gives those resource collectors a chance to make some extra money from what they collect. Botters have put the prices of a lot of items down, bonus XP weekends restore prices (temporarily) back to what they should be, which I think gives some fair game-play for those who provide resources in the Grand Exchange that do not bot. In addition, not everyone is capable of playing in that one day - it would be a tad unfair if it had to span over 1 day because not everyone will get an even chance, with the most recent bonus XP weekend, everyone was allowed the chance to reach the lowest multiplier.