Back when The Office was still about how dull it is to sell paper for a living, Jim and Pam would pull pranks on Dwight or spend their time flirting at the reception desk to alleviate the boredom (obviously, Tim and Dawn from the original are the models here, but that run was so short that we never got to see them become insufferable). Because Dwight is an easy target and an alienating figure in the office, the coworkers put up with the nonsense, but Jim and Pam have never really been too interested in getting to know anyone else beyond work (except when they feel guilty about something, then they'll do something nice which is just as much about doing the right thing as it is about making them feel like they are good people. Contrast that to Michael Scott who, while childish, legitimately cares for everyone. Except Toby).
It was easy to ignore that Jim and Pam were actually kind of mean because the show wasn't so cartoonish. It really did feel like people were trapped in this office and any respite was needed to maintain sanity. Plus, the early years of the relationship were relatable. Who hasn't had a crush on someone who wasn't available? Who hasn't been stuck in an unfulfilling relationship? The viewers can relate to them and root for them because there's a very obvious connection between Jim and Pam that was never there with any of their other partners (to be fair, there are those who found them insufferable early on). I count myself among those who audibly gasped when Jim finally kissed Pam. It was an exciting moment when the show was at its peak.
The Office eventually started throwing up roadblocks both organic and contrived. Jim going to Stamford was a good move. Pam going to New York was OK, though I suspect she probably would have gone to a smaller program somewhere closer. Pam flirting with a classmate felt like an excuse to make Jim insecure (though she did have a history of flirting with friends while in a relationship). It's around this point that the Jim/Pam courting plot line was getting stale. Finally, they got married and had a child and the show hasn't known what to do with them.
Jim and Pam have always been selfish, but in the past, we had a reason to root for them. They needed an escape. They needed each other. Now that they're together, it's like there's nothing for them to do but feel superior to everyone else. The writers on the show keep trying to set up more Jim and Pam-like scenarios with Andy and Erin or Daryl and Val. Relationships with obstacles to overcome (the obstacles always seem to be that one of the characters is already in a relationship with another person). We don't need another Jim and Pam. Come up with another approach. The Phyllis/Bob Vance union was terrific. The Office seems to think that the only people you meet and love are those you meet in an office.