I removed one row of shirring from this OP and rescued it from the "to sell" pile.
Wardrobe turnover, for me, happens for several reasons. The first, and sadly the most common, is when I've bought something without actually thinking about how it would look and me and how comfortable I would be wearing it. For example, it took me a while to realise that though I loved straight up sweet lolita on other people it was not something I was comfortable wearing myself. Fortunately, the longer I spend in the fashion the rarer these mistakes become.
The other main reason I sell items on is because of fit issues. A prime example of fit was my Loyal Rosette JSK. I adored that dress and it was perfect in every single way except how it fit on my body. So I sold it on. Unfortunately, fit is something you can't know until you have the item in your hands. Even if you have experience with a brand and get the hang of which of their cuts generally fit well on you you still can't be totally sure.
Lastly, issues of quality also lead me to get rid of items. By now I mostly have fairly good quality items that I'm happy with, but especially when I started out I bought and made a few things that weren't the best. I have a better eye for quality, and more experience, but again when you buy online you can never be totally sure of quality until you have something in your hand.
For the rest of this year [and for all the rest of my lolita-wearing years] I'm hoping to mostly add keepers to my wardrobe. I have a large-ish to sell pile at the moment, but once that's gone I'm going to try to be very selective in what I add to my wardrobe and hopefully get it to a state where it's a great collection for everyday as well as special occasion clothing.