A previous employer hit the problem where there were a ton of legacy features that didn't have clear owners and so it wasn't clear where to route bug reports.
Their solution was to build a catalog of every feature and then assign EVERY one of them to an existing team.
Teams might end up responsible for features that they had never seen before and had no knowledge of... but that was fine, because every other team was in the same situation.
It worked great. Bugs got fixed. Teams figured it out.
The truth is that accountability isn't the problem, its the lack of resources, prioritization, and ability to change things that make them burdensome. After a certain point you're just trying to solve the problem in the least annoying way possible.
Their solution was to build a catalog of every feature and then assign EVERY one of them to an existing team.
Teams might end up responsible for features that they had never seen before and had no knowledge of... but that was fine, because every other team was in the same situation.
It worked great. Bugs got fixed. Teams figured it out.
Team owner leaves or is let go and then their projects get randomly assigned to other people.
That's not terrible. What is terrible is when there is no mechanism for swapping or trading projects.
Just pick someone and give them the task.