hat I cannot work out is, why would people want to be ranked below another site using the same title?
Let's say you're number one in the SERPS, and the competitor of yours is #9. Even if they didn't get ranked above you, #2 would get them a lot more clicks than being #9.
Are we all at risk of having our titles reused?
At this point and time : yes. Some of the engines are working on identifying multiple content (the same title, description, etc on multiple pages), but there are still flaws since the engines have no way of telling who to penalize for the stolen content.