Because eBay has a message for sellers in the Seller Hub that tells the seller there are items eligible to send offers. Sellers get that message because the buyer has shown interest in the item by clicking on the listing, adding the item to their watch list or cart.
I don't know why eBay isn't responding to you, but then how are you contacting eBay?
eBay doesn't respond to eMails and doesn't have a phone number for you to call. The only way of making contact is to start a live chat or receive a call back through Contact Us at the bottom of the Help & Contact page.
