Why is that?

The only inconsistency is the word "might," which can be translated as "strength" or "power." The title actually implies that the game features both magic and power (i.e., strength of a non-magical, but physical nature). But can you imagine what it would be like if the game were called "Heroes of Power and Magic"? It's somewhat reminiscent of a poor, pirated translation. Therefore, the concept of power was characterized by a sword – the main weapon of the Middle Ages (the heroes are set in a medieval fantasy world). Again, something like "Heroes of the Hammer and Magic" or "Heroes of the Mace and Magic," and other similar options, would sound awful. The localizers (specifically, Buka) found the optimal option.