Why do conversations get removed?

So, as the title states... I'm trying to figure out why conversations get removed when someone deletes you from their friends list, or when you delete them.

I just had a player add me after a game and spout line after line of nonsense, being extremely nonsensical and toxic. I'm aware that players can be reported manually Via a support ticket, so that was my intent.

While filling out the support ticket, the player in question continued to ramble on. Right as I went to copy the conversation for the ticket, they deleted me. Yay, the player is no longer on my list... Except, WAIT! Where's the conversation I was attempting to copy? Oh, it's gone? Why?

I understand removing the ability to communicate with someone who deletes you, that makes perfect sense. Totally removing the conversation and all history of it WHILE I'm reading it though? That's just not necessary in any way. Why remove our entire log of a conversation, just because we aren't "friends" anymore? It really doesn't make sense to me.

I've also in the past had a friend tell me their main account name(I had met their alt and added it.), before clearing their friends list. It took 2 months before they added me complaining about why didn't I add them - I never even got to see the message saying they were changing accounts, due to the conversation being deleted when they cleared their friends list.

So I guess what I'm asking is: What reason is there for fully removing conversation history, just because a friend was deleted? There's plenty of reasons that the history might still be useful to a person, even if the friend is no longer a friend.