Hi @JRuss, I'm responding from my home account. The earlier one was from my work account.
The "stay in your own lane" mentality is an unwritten rule. It's a sense I get from what I've observed. I've already given you an example of my not being able to suggest something to DBAs and vice versa. Another example is meeting with customers (all internal, in my case) to learn what it is they want done, how some old application works, how they'd like a new one to work, etc. When I first joined my current employer, all developers weren't allowed to meet with the customers. Instead that activity was done exclusively by people in our Project Management Office, normally Business Analysts (BA), whereas developers and DBAs were relegated to stay in their office/cubicles (this is all pre-pandemic). Developers were expected to bang code, DBAs to write SQL scripts, do database administration, etc. Then once the BAs had finished meeting with the customer as often as needed, written up the specifications and other documents, then DBAs and devs would get the specs and docs and start doing their work. Everybody does what their job title is and don't interfere with others with a different job title.
In fairness, that has begun to change. About two years ago devs and DBAs were invited to participate in some meetings with the customer, normally early in the project planning process. So, in this regard some progress has been made. But still, there's a stay in your own lane mentality. The BAs do the database design, which I think is a shame. One of the senior DBAs told me that he had taken some advanced database design classes, but it's all for naught, as he can't use that training. The BA designs the database, then hands it off to the DBA to implement. If that DBA finds something egregious in the database design, he can bring it to the BA, argue his point with the BA and I hope it gets implemented. But it's the BA's job, because it's related to writing up the spec and documents, which BAs do, and DBAs and devs don't.