Simply because there is no point in selling them anyway. Its very cheap as if its worthless. Also most of them are not listed anywhere so there is no way you can get rid of them. It will remain on your wallet whether you like it or not. You'll never know, one day when you wake up, your coin might have some value. But don't keep your hopes up. Better move on.
On shit coins generally can not get hung up their our attention. If you once were lucky, and you successfully traded some sort of shit coin, this does not mean that it will always be like this. In any case, you need to quickly get rid of overt scam coins.