Two things: 1) someone could have closed their account & it doesn't have anything to do with you, and 2) perhaps they had favorited your items as a part of a gift idea (envisioned your product as great, but just for someone else) and now that that birthday or event is over, they are purging the friend favorites.
I've definitely done that before - it didn't really reflect much on the product. The other thing that comes to mind: my friend has a shop and will only favorite things that fit into her business personality. When she decided to make sure everything from her favorites to her website seemed cohesive, she unfavorited a bunch of things that just weren't right for what she wanted to present. I, personally, didn't think it mattered to do that (if you like it, you like it, who cares?!) but she did it.
See... lots of reasons for fewer hearts and none of them are about you!
