The rest of the cast is... less fascinating
This wasn’t so much a problem in season one, when House of Cards had Corey Stoll and Kate Mara at its disposal. Peter Russo might be the only genuinely sympathetic character the show’s ever had, and Zoe Barnes -- well, I kinda hated Zoe Barnes for taking the already-exhausting pop-culture trend of slutty, manipulative lady reporters to new heights, but she definitely wasn’t boring!
Those two have been gone for a long time, though, and the show seems to be suffering under the delusion that we care just as much about the remaining supporting characters. Characters like Zoe’s mopey ex-boyfriend, some old rich guy who collects birds, and Doug Stamper, whose entire season-three plotline can be summed up as “sad physical therapy, followed by continued stalking.” The problem isn’t that these characters are hard to like (although they are). It’s that none of them are remotely as interesting as the two leads. And that’s a shame, because the show employs some pretty excellent actors with little to do but creep around government buildings.