It's difficult to distinguish genuine romantic feelings from exploitative lust everywhere. It's a constant of human experience and has very little to do with power dynamics.
Huh?
Where there's a power imbalance, it's easier to ban a class of abuses than to figure out the small percentage of cases where both parties are genuinely afflicted by mutual biological imperatives.
How would you, an outside party, determine whether the superior was really [infatuated, in love, whatever], and not simply taking advantage of their situation? Or how would a judge determine that? Is it worth it to the company to work through that process every time it happens? What about the people who really were victimized, but the evidence is circumstantial and the court says otherwise? Isn't it easier to exclude the small pool of people that are subordinates and tell the supervisor to find romance anywhere else?