Key takeaway
Diffuse ownership isn't a shortcut, it's a guarantee that everyone will rationally assume someone else has it.
It is tempting, especially early in a project, to leave a task's owner as "the team" or "design," rather than naming one person. It feels inclusive, and it avoids the slightly awkward moment of putting one name on something that several people will actually touch. It also almost guarantees the task will slip, because nobody individually feels responsible for a deadline shared by a group.
Diffuse ownership is not really ownership
When three people could plausibly be responsible for a task, each of them can reasonably assume one of the others has it handled. That is not laziness, it is a completely rational response to ambiguous responsibility. The task does not get dropped because anyone is careless, it gets dropped because everyone was individually right to assume someone else had it.
One name, always
Every task should have exactly one owner, even when several people will contribute to it. The owner is not necessarily the person doing the work, they are the person accountable for it getting done and for flagging it early if it will not. This is uncomfortable to enforce at first, because it means asking "who, specifically" more often than feels natural, but it is one of the cheapest changes a PM can make to how reliably a task list actually gets executed.