They use the events because marketing told them that SDX drops don't force players to be online, on the game for hours at a time to get them. These events force you to be online to play the game... because they have packs to sell. There's an entire study and psychology that centers around how much time a person needs to be on the app in order to make an in game purchase, that coincides with the science of how often a person needs to be reminded that there is a dlc they don't own and be shown an ad for it. This is about marketing... I'm a marketer, I know. It's genius really. If theydevise some random quest that requires you to be online for a minimum of a certain amount of time, while simultaneously showing you ads to buy something... you are more likely to buy something.