That's all correct in theory, but in my experience these things still happen and are usually outgrowths of bad engineering culture / shadow IT / not wanting to be reliant on your cloud infra / platform team (often for irrational reasons, sometimes not). They get built with entire teams taking responsibility on paper, but then before you know it, nobody from that team still works at the company or on that team. Usually these systems are also GDPR nightmares if they contain user data, because these people don't understand when you tell them they need to have a plan for deleting user data. They don't even consider it a legal barrier, they think you're putting stones in their way.
I've been on enough Cloud Archeology expeditions into the land of VMs where nobody knows what they do, it might as well be my job title now.