I have seen many front-end development frameworks that are simple a collection of UI components and page layouts to be used by developers to build new applications. However, it should come as no surprise that simply having a consistent collection of components doesn't guarantee a consistent feel (you might have the looks) because there are 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 realized that there were a common set of problems that can be solved by a standard (generic) set of interactions that are agnostic of the UI components. And when you combine define the design patterns with the UI components in your development framework, you then have a more consistent way of implementing the user interface (at least in my opinion).
So why is it that design patterns are often not part of the design system? I am still curious as to why style guides and development frameworks continue to exist as separate entities (most of the time) when something like design patterns could help improve the consistency of the design.