Ninjala...I think is a free to play game, so not sure why there are physical copies being sold.
They usually give you some cosmetics and in game currency, they do it because they get sales. Fortnite did. Some Grandparents, uncles etc know that kids like it so they buy it when they see it on stores shelves. Easy sales so it will keep happening.
TLDR: Store Shelves= visibility and extra sales compared to digital only.