I have mixed feelings about this. On the one hand I agree that ownership should be shared. On the other, app developers really don't consider their data structures as carefully in SQL as they do in-memory. It's odd. The right data structure matters more than a good algorithm since algorithms are easier to change. Once you settle on a list vs a set vs a queue, you're stuck once code is built around it.
The same is doubly true for the database schema. Lack of planning and knowledge of expected access patterns can turn an otherwise fast database to mud in no time flat. Once your data is in there, changing the schema is exponentially harder.
"I’m a huge proponent of designing your code around the data, rather than the other way around, and I think it’s one of the reasons git has been fairly successful… I will, in fact, claim that the difference between a bad programmer and a good one is whether he considers his code or his data structures more important. Bad programmers worry about the code. Good programmers worry about data structures and their relationships." – Linus Torvalds (2006)
What is your database but a bunch of data structures and relationships? I get why the gatekeeping occurred. I don't agree with it, but I understand it. Far too many folks consider expertise in data stores to be optional as developers.