eInk screens are extremely fragile. You can break it with very little pressure using only one finger. If you read horror novels and get bitten by a mummified minotauros and you hold your reader in a death grip while doing so ... crack.
It's the major downside of the technology and with every new generation of readers I'm hoping for them to gain unbreakable (flexible) displays, but alas, it's not happening. Probably too expensive or other issues.
If you sell it on Ebay you might get 20€-ish for it [at least they were that expensive when I tried to buy broken ones for my firmware experiments), some people buy it for replacement parts (like if you manage to damage the USB socket or whatever) or just for the electronics... or maybe they're hoping to find a large ebook collection
