That question goes straight to the core of why those stories are so impossible to put down. The central conflict is almost always a brutal collision between primal, biological fate and cold, calculated human intention. The 'mated' part screams a destined, soul-deep bond that’s supposed to be all-consuming and involuntary. The 'by contract' part is a deliberate, often mercenary, transaction that denies all that instinct.
You get this excruciating internal war where the characters are physically and emotionally drawn together by a force they can’t control, while their minds and pride are screaming at them to resist because the foundation is a business deal. The Alpha, used to total dominance and obedience, now faces a mate who is legally bound but not willingly bound. His authority is both affirmed by the contract and completely undermined by her resistance to the very bond his wolf recognizes.
It creates this delicious tension where every act of care or protection can be read as either fulfilling a contractual obligation or a genuine, unwanted step toward the bond. The denial from both sides, the constant questioning of motives—is he helping me because the contract says he must ensure my safety, or because his Alpha instincts are taking over?—that’s the engine. The emotional payoff is the slow, painful erosion of that denial, where the contractual lines blur until they’re meaningless against the pull of the bond they tried to commodify.