It's a great question why would a eBay reseller even bother with blogging, especially if they have a great social following?
Simply more sales. Thats why most webpages exist for more sales. The almighty Dollar. Keep in mind it's not because you are a fascinating fellow that has adventures daily. It's because you need to increase your sales. Even if you have a bunch of repeat customers, to grow you need new customers daily.
There is an art to getting new customers daily. Give them something they want, especially if it is something they didn't even know they wanted.