There are certain kind of stories where the goal is to create drama, but not so much that you’d have to change characters, locations, or even relationship dynamics. I’ve come to start thinking of these as “soap plots,” in that the goal is to complicate the characters’ lives while avoiding any overall story change. (The origin of the term, of course, comes from soap operas.)
This is different from a story that is about dramatic relationships – who slept with who, who had whose baby in secret, and so on. While these might be stories that are featured in “soaps,” if the plot causes the story to change on any macro scale – new location, new conflicts, new themes, new characters, etc. – then it is not, by definition, a soap plot.
Poldark on PBS is the most recent one of these. PBS Masterpiece shows seem prone to these plots: while being ostensibly about the changing times, Downton Abbey steadfastly refused to change much, and resorted to ludicrous legal complications (rape, dead rapists who died under strange circumstances, ex-wives who died under strange circumstances, and so on) to keep the character relationships exactly where they are. The overall experience was a lot of stuff going on, and yet nothing was happening. The choices do not matter, which means there are no stakes.
Poldark is similar in that it keeps throwing obstacles in the way of the characters to maintain a lot of the same dynamics. Though the story is based on a book series, and thus has to keep to some character mixups, there are times that the characters make intentionally stupid choices just to maintain status quo.
One show that found (or was forced to find) a way around this is Halt and Catch Fire, which essentially built a whole new show every season, skipping forward in time to find that a lot of the character dynamics had totally changed and telling a whole new story. Mad Men and The Wire figured out the same methodology. It’s a device that acts as a service for the writer probably even more than the reader: by totally eliminating the option to do the same old same old, you’re forced to innovate.