These are not additions to "Bitcoin Core" by which I assume you just mean the Bitcoin protocol. These are optional things that people have made that use an unintended loophole in the protocol to allow data to be jammed into transactions and used as NFTs.

There is no justification. People figured out it can be done so they did it. I don't even know what you mean by justification.

They were created because people in the community recognized the flaw the update to the protocol would allow such things and so they took advantage of it to create these things. Yes they make the network less efficient. And no they don't have anything to do with Bitcoin being money so they don't help Bitcoin be a better monetary system, rather they hurt it being that. But the people who made it and use these things are more concerned about NFTs than they are about Bitcoin as money, so they did it. Nothing to stop it now unless the protocol devs do something to close that loophole that ordinals exploited.