he 19th century European concept of marriage as depicted in Wuthering Heights is largely based on social and economic advancement and not, as it is in modern America, a romantic notion. In other words, couples married to either maintain or advance social class or property (land), not because they necessarily loved each other.
Most of the characters in Wuthering Heights are members of the gentry (upper middle class), one step lower than the aristocratic class. On the heath, the Lintons are more well off than the Earnshaws. And the Earnshaws are more well off than the orphaned Heathcliff. So, Catherine Earnshaw marries Edgar Linton to become "the greatest woman in the neighborhood." She moves over from Wuthering Heights to Thrushcross Grange for socio-economic advancement. Even though she loves Heathcliff (the romantic concept of marriage), she marries for a better house and more land.
Heathcliff resents the concept of marriage to no end. Even though he turns himself into a member of the landed gentry, he is still forsaken by Catherine and the society. So, he plans revenge on the entire system: he abuses the concept of marriage to acquire both houses (Wuthering Heights and Thrushcross Grange). He arranges marriage between the younger Catherine and Linton as a cruel punishment to this second generation on the heath. His goal, I think, is to destroy the (romantic or economic) institution of marriage by abusing it to its extreme end.
Unlike modern America, the 19th century European concept of marriage was largely based on social and economic advancement. Marriage has no value in the novel Wuthering Heights. It is a contract, an obligation. Cathy marries for money, Heathcliff marries Isabella so he can inherit her land.... both of these marriages are entered into for financial reasons