It is a new patent and the original can made generically once the old patent expires. Marketing is the difference. For example, you may have seen people talking

It is a new patent and the original can made generically once the old patent expires. Marketing is the difference. For example, you may have seen people talking about the excessive price of insulin in the US, but they ignore the fact that you can still get the old versions for very cheap. It's also done with "extended-release" versions of the old version.