maybe a burner address or some unconcerned billionaire's long term savings.
This address ever send Bitcoin to other address, pretty sure someone know the private key and have control of this address, so it's not burner address. It could be someone savings, but it much likely the owner have lost the private key. Selling only 1 Bitcoin from 31000 Bitcoin won't hurt you lol.
I doubt when someone can know a private key of an address contained really a lot Bitcoin in the moment still want to give it back
