In my experience, when developers start bringing up "maintainability" during feature discussions or code reviews it has less to do with a particular feature (though that might be what prompts the discussion) and more about the current state of the product.

Sure, we as for-profit developers write code so that, ultimately, it can generate revenue. But if work is only ever allocated to pursue immediate business value, the team may find itself slowly drowning in technical debt. New features take longer and longer to develop, and often it's hard to point to an exact cause of the problem, leading to debates about the "maintainability" of single features when the real problem is the product as a whole.