A big part of the Bob's Burgers appeal is seeing the Belchers as a cohesive family unit.
Consider the environment in which Bob's Burgers dropped. You had the Griffins, who openly hated each other. You had American Dad, which by this point had devolved into Roger being willing to kill the entire family if it meant even the slightest benefit to him. You had Rick and Morty, which has become a tedious morass of slef-loathing and bitter nihilism that mocks the idea of things like love and caring.
Animated TV families had gotten nastier. Then Bob's Burgers comes out, and it's novel because here's a family that actually loves and supports one another. Linda is wild about her "Bawbby", and they have an active sex life where they're both still very attracted to each other. The kids all get along well to the point that any fighting is seen as abnormal. Even Louise, who started out as supposed sociopath, has matured more into a rebel with a cause, standing up for her brother and sister when someone, usually an adult, cuts them down
Animated sitcom families for the better part of a decade were shown as dysfunctional to the point of imminent collapse. Seeing a poor, but stable and loving family struck a chord with a lot of people.