Same Old Story : TV Plots

There are great television shows like Castle, Downton Abbey, and Once Upon A Time where a tiresome repetition occurs.

     Despite the witty dialogue, creative storyline, great casting, famous cameos, and convincing delivery of script, you still wonder what's wrong with the writers.  Why do they overkill the same plot device?  Each show's main couple attracts each other, they get together, they break apart, they get together, they break apart.  Then, they get together.  And break apart again.  
    That routine wears out its welcome.  I've heard from so many people that such "tricks" frustrate them and cause them to stop watching the show.  Don't the writers/creators realize that if they keep doing that--each season--the audience might lose interest in the characters?  It's like "the boy who cried wolf".  
     Maybe the writers are inspired by daytime soap operas (or they're hoping for that kind of addicted audience--who'll believe anything).  But, there are numerous popular TV shows that happily move ahead with their couples.  They actually make progress, once the couple is united.  Shows like Modern Family don't rely on breaking apart/reuniting their main characters.  Other shows like Law & Order don't even bother uniting characters in a love interest... yet they (and shows like them) remain popular.
     I think that there are numerous plot devices and storylines that could be implemented to progress things, instead of "falling back" on such repetitive tactics.  After a few seasons--when the characters unite--they could work together to overcome new challenges.  Their dynamics could change, and they could develop further as characters.  

     It doesn't seem fair to the audience's patience to make them re-watch a worn-out subplot... just because its convenient for the writers.  Or perhaps the writers need better inspiration.  They will get success with better writers.