Knife crime is more of an issue where guns are not easily accessible, such as in Japan or the UK. It is as @jacobtothe has been saying this whole time: people with violent intent will use whatever they can get their grubby little paws on to commit violence. The underlying cause of violence needs to be addressed, not the implements used to commit it.

Edit: also, I have seen this deliberately misleading graph before. It omits children under the age of 1, because if it didn't, firearms would no longer be the leading cause of death.