Quick: Close your eyes and think of your favorite TV shows. You're ... you're thinking of 19 Kids and Counting or some shit, aren't you? Fine, let's just look at this list from Rotten Tomatoes, instead. What do you notice?
Besides the fact that you've been spelling "Downton" wrong all these years.
The most beloved shows out there have long murdered the "story of the week" format so ingrained in '90s television. Game Of Thrones, Mad Men, The Walking Dead, Better Call Saul, and even more episodic shows like Archer and Agents Of S.H.I.E.L.D. maintain a throughline thicker than The X-Files ever did ... at least until the writers started injecting a longer-running story, which was right around the time people stopped watching it.
It didn't help that Mulder and Scully were replaced by two very disappointed teachers.