Why are gooseberries called gooseberries?

The exact reason is not known but many expect that it is a corruption of the old german, french or dutch names for the plant. However, it is also likely that it was just named "gooseberry" and not actually a corruption of another word. Many plants have been named after animals for no apparent reason such as fox grapes and buffaloberries.

according to wikipedia

The first part of the word has been usually treated as an etymological corruption either of the Dutch word Kruisbezie or the allied German Krausbeere, or of the earlier forms of the French groseille. Alternatively the word has been connected to the Middle high German krus (curl, crisped), in Latin as grossularia. However, the New English Dictionary takes the obvious derivation from goose and berry as probable; the grounds on which plants and fruits have received names associating them with animals are so often inexplicable, that the inappropriateness in the meaning does not necessarily give good grounds for believing that the word is an etymological corruption.