Marge Simpson (Lois Griffin, Francine Smith, etc.) is a housewife/mom. She does housewife/mom things. Passive, backseat of most plots.
Linda Belcher is a person. She does Linda things. Active, lead of many plots.
Linda seems most like she has an actual personality, she's confident (confidence is always sexy for anyone), her opinions mean something, and she isn't just some empty shell of a person who waits for you to give them meaning.
Women love her character because she's confident and active, takes charge of her own life, and does what's necessary to get the things she wants in life - all things the average woman desires, yet believes to be impossible to achieve through work and practice. Linda is like a superhero to them, naturally born interesting and confident, like everyone's favorite male characters.