Artifacts, true artifacts that is, seem to have a mind and will of their own, and rarely stay in the same hands for long. As the player, you are essentially "destined" to receive them, though whether this is due to the hero being doom-driven, or simply the machinations of Daedra, or any number of overlapping surcumstances, is up for debate. It is worth noting that in most cases the Daedric quests to receive these artifacts are not open to any old schmoe who is out wandering in the wilderness. They are only open to the hero. For example, in Nocturnal's quest in Oblivion, it could perhaps be suspected that the quest was merely a ruse, an attempt to put the Skeleton Key in your hands without making it seem like she was just giving it to you. Perhaps in Meridia's quest in Skyrim you didn't simply come across her beacon randomly. Perhaps she purposely plopped it in front of you so that you could clear out her temple.
In conclusion, the Daedra are sneaky gitz.