By modern, I also mean they follow a continuing story arc episode-to-episode, so while you could watch any episode in isolation, you get a lot more if you know backstory and the characters. They're also all "single camera" shows (no laugh track) which IMHO is a much better style, and allows them to be more creative, have a continuing story, and frankly, be funnier than the (pause for laughter) lines in a show like Big Bang Theory.
To me, even the most "everyday" of those fall prey to the usual U.S. tendency to elide class at all costs - even the no-good slackers in a lot of these shows seem to have the comforts of someone in the top 20%.
Last weekend I watched amazon original 'catastrophe' and 'lilyhammer' a netflix original. Both of these revolved around ordinary people doing everyday stuff.
(I do, however, very highly recommend the series. I've only seen Season 1, but it was fantastic, and the character's slow immersion into the local language and culture was very well done.)
The Office went through all of its kooky manager plotlines because Steve Carell's career trajectory outpaced the show's initial popularity. The second he got too big for the show, everyone knew it, and much ink was spilled in the writers' room trying to anticipate and/or compensate for his eventual departure.
Jim was given some upward mobility because he's the protagonist, and the audience was rooting for him (and Pam) in a personal way. Nine seasons of Jim's being stuck in a dead-end paper sales job, with no hope of escape, would have been extremely depressing. I realize that's how the UK version chose to play things, but it would have been too bleak by half for the US market.
I think the main artistic factor here is that the sitcom, an awfully convenient medium for telling middle class stories, is dead. A 30 minute comedy where every episode was basically an island could be an oddly touching medium to talk about a teacher dying or a dad losing his job. But these tiny canvases were mostly the result of the constraints of 20th century TV.
Without those constraints, consumers don't have that much interest in slices of everyday life, just as most consumers don't read Raymond Carver stories. Our imaginations go to the rich, powerful and supernatural. I'd argue that other mediums - podcasts, reality TV, social media - fulfill the basic human need behind the sitcom: to simply bask in the company of agreeable/relatable sounding human voices.