It’s true that the meanings of the sentences are rarely related to those of other sentences. They don’t make full dialogues. This is because long real-life dialogues don’t allow the kind of structure that is needed for spaced repetition.
However, they’re not random because they follow a plan. Certain words are repeated during each lesson and, more importantly, throughout the course. Grammar patterns are repeated intensively during each lesson, and add up throughout the course to build complex sentences. Vocabulary goes from basic to relatively advanced. Grammar patterns go from simple to relatively complex.
As a result, after the course, you’ll be able to communicate because you’ll have learned how to handle the elements of virtually any sentence you might want to say, not limited to the sentences you heard in the course.