Well Nightwing/Grayson has never been a strong merch seller. So it isn't that surprising he wouldn't get anything now. It just isn't a big focus. Batman, Joker, Harley, Robin, Batgirl and maybe even Red Hood are stronger merch sellers I'd bet. All of his looks and costumes, especially Nightwing, have been basic and doesn't really grab people the way the designs of those other characters have.