I love this thread, too -- it is so useful to think about the reasons our things go unworn.
So far, most of my unworn or little worn spring/summer purchases are casualties of the cooler than usual weather, and I fully expect and intend to wear them as soon as warmer temperatures arrive. That list includes one sleeveless top, a tee shirt or two, and my new shorts. Not too bad, really.
My only genuine dead horse item is my sage green Gap broken in khakis. I've worn them maybe once. They just don't appeal to me a whole lot. I can't say why. Maybe it's simply that I like my various jeans so much better! All is not lost, though. First of all, I got them on massive sale. And I have a feeling I'll enjoy them a whole lot more as BF shorts, which is what they may become before summer ends.
Another possible dead horse in the making -- my Clarks metallic wedges. I got them at a super bargain. (Hmmm. Are you seeing a pattern here? SALE BLINDERS!!!) And they seemed good at first. Lightweight. Comfy footbed. Pale almost nude metallic. Etc. But they don't fit me properly (too big) and they feel a bit clunky and they just aren't quite what I was wanting. I may have to offer them up on the exchange.
Also, Rae, I have to reluctantly high five you and confess that I haven't worn my Leith pants a whole lot. They have come out to play a few times, but I tend to consider them and put them back a lot more often than I actually wear them. Again, they might get more play later in the season. They're quite lightweight and it has felt too cool for them a lot of the time. But I'm watching this development with interest.