Without the surrounding and supporting, end-to-end learning organization, an encapsulated team - even if it has begun to turn itself into a learning culture - will sooner or later begin to under-perform. It may even degrade to a point of becoming largely ineffective, leading to re-organization or disbanding.
Continuous improvement is the goal of a learning culture. Like the mechanics of a learning culture, the mechanics of continuous improvement isn't an ad hoc series of suggestions from on high on potentially better ways of doing things, or merely random trial and error acted out by workers in place of dealing with higher priorities.
Continuous improvement is a managed process. Improvements are done with the aim of creating systemic optimizations. The terminology from the Toyota Production System is, "optimize across organizations." Making local improvements without considering their impact on the whole system is hacking rather than improvement.
Each improvement is a change. It creates a new set of conditions. It changes the system. At a fundamental level, improvement creates a new system, albeit with a great number of similarities to the previous system.
The conditions created by a previous improvement aren't perfect. They're likely better than the previous conditions, but they are also inevitably the pre-conditions for the next improvement.
Conditions created by an improvement that create the potential for the next improvement typically aren't predictable. We have to make an improvement and then live in the conditions that result, observing them, remaining vigilant for the next improvement, and being watchful for undesirable local optimizations.
Each success creates the next set of conditions that, if not dealt with, can become the next failure. This cycle is why improvement is necessarily continuous.