You know, scrolling through the recent threads on romance and paranormal forums, this question pops up constantly. I think it's a lot simpler than some of the deep psychological analyses suggest. It's about wish-fulfillment in its most direct form. Life is chaotic and often feels unsafe; a story where the lead's entire being is wired to prioritize the heroine's safety above all else, with the power to back it up, provides a specific kind of emotional vacation. It's not about control in a toxic sense—at least in the well-written ones—but about a hyper-focused, unwavering sanctuary. The appeal lies in the fantasy of someone so capable that the outside world's threats just... bounce off. It's the literary equivalent of a safety blanket woven from competence and brute force.
That said, the execution is everything. When it's done poorly, it feels stifling and the heroine becomes a prop. When it's done right, like in some of the better omegaverse or fantasy protector romances, the 'alpha' aspect is less about dominance over her and more about dominance over any threat to her. The dynamic works because her strength can be in other areas—her intelligence, her resilience, her kindness—while his specific toolkit handles the physical or societal dangers. It creates a complementary partnership where she gets to be soft in a world that usually demands hardness, because he's the hardened shell. I keep coming back to that feeling of narrative safety; it lets you relax into the romance without the constant anxiety for the characters that other genres thrive on.