Why are design models not normally included in a design system?

I have seen many front-end development frameworks that consist of a simple collection of user interface components and page layouts to be used by developers to create new applications. However, it should not be surprising that the mere fact of having a consistent collection of components does not guarantee an impression of consistency (you may look like it), because there is still a myriad of possibilities when it comes to implementing a set of interactions on a page.

Design patterns were popular in the early days of UX design, when designers understood that there was a common set of problems that could be solved by a standard set (generic) of agnostic interactions of the components of the design. 39, user interface. And when you combine the definition of design templates with the UI components of your development infrastructure, then you have a more consistent method for implementing the UI (at least in my opinion ).

So, why are design models often not part of the design system? I am always curious why style guides and development frameworks still exist as separate entities (most of the time), while reasons such as design patterns might help to improve the consistency of the design.