It could be anything--as others have said.
On the other hand, maybe its something about lack and supply. In other words, when something you lack, comes into supply, because you lack it and want it, and its suddenly in supply, maybe it causes you concern: will it ever be available again? what if it isn't? etc... and then you obsess...
Maybe you could take comfort in the idea that all the bags you ever want or could ever need ever are in supply at least for now, in virtual form.
Since you seem to change your mind about colors etc, its just as well that you aren't buying them right now....right?
Maybe if you focus on collecting the "idea" of the "available bag" instead of the actual thing, (just for now, I know the goal here is to get a bag), you can at least satisfy that collection urge until you get the funds together for your bag.
I take an enormous amount of pleasure in seeing everyone's reveals. I have a few bags, but I realize that when I look around at everyone else's bags, they all look fantastic and I want all of them. But I don't really....
Hope that this helps...