To be clear, it's lost XX% of it's market cap. The market cap is a knowingly-flawed assessment of earnings potential for a company. Its actual value is probably unchanged.
The value of Etsy changed when Amazon entered its space. It is objectively worth less now that the 800 lb gorilla has decided to eat Etsy's lunch.
The real issue in my opinion is that Etsy discovered that they couldn't keep growing without opening their doors to cheap non-handmade shit. Which they've done. And their search/discoverability is absolutely awful.
My partner lists her truly handmade products on Etsy but only as an afterthought. As the amount of garbage on Etsy has increased, her views/sales have dropped. She has put all of her effort into getting sales through her own website, where at least she's in control.