cynical take. you need to define who owns what, otherwise you have people who assume and have expectations without communication which leads to even bigger issues and resentment. it's not unlike a romantic relationship
A Role-level definition severely limits one's ability to grow, get holistic/big picture view and leading to "That's not my job" mentality, all because someone arbitrarily put a line, not dissimilar to culture or standard of living differences between arbitrary political lines.