A consultant named Nils Pihl believes that video game players have a natural tendency to ruin the titles that they play and says that the best example is the grenade spamming phenomenon that appeared in Call of Duty: Modern Warfare.In an in-depth Gamasutra feature the consultant says, “Random interval reward schedules can be incredibly addictive. The fact that you didn't know if you would hit an enemy or not turned throwing the grenade into highly addictive gambling scenario. All you had to wager was a cheap grenade, and you could win very desirable points in exchange.”
The combination of low cost and addiction meant that soon almost all the players were spamming grenades.
The full feature goes into more detail about how dedicated player communities tend to create mechanics that sabotage their own experiences and uses Starcraft II as a counterexample.