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.
But Etsy struggled with leadership and technical problems in those days that were really serious, and not easily solved.
In 2005 Etsy's advantage was that creating your own standalone shop was hard, expensive, and ineffective. They shuffled CEO's while Shopify, BigCartel, WooCommerce, BigCommerce, and many others solved those problems. And Kickstarter proved you could make a lot of money without losing your cool indie cred.
There has always been a disconnect between what Etsy wanted to be (and there have been multiple versions of that) and what it's sellers (who are its customers) wanted. That grew into a chasm so big that Amazon saw light shining through it.
I have two gut feelings:
1. Hobbyist Etsy sellers don't dedicate the time and/or lack the business savvy to be running additional sales channels outside of Etsy. Additionally, even setting up a Shopify, etc. store requires some technical ability that you or I take for granted.
2. Semi-professional Etsy sellers, for example, those coming from operating eBay or Amazon Stores, were already using their other channels before Etsy. So they were sophisticated enough that it was cheap/easy to have someone whip up an osCommerce + PayPal site for them. I did this personally for a few clients already successfully selling on forums between 2005-2008.
Peak $34 in May
down to $14 in July
bounced but back to $14 in August
flat till October when Amazon entered now down to $7
Jeff Reeves at InvestorPlace [1] caled it "the biggest joke on Wall Street in May"
See: search, auctions, classified ads, smart phones, etc.