This is a good rundown of (the history of) the appeal, particularly to male viewers. I hesitate to call the melodrama "incidental", though, as the female viewers it drew in were the ones who saved the franchise (per Tomino) when it initially failed to take off. The creators recognized where their bread was being buttered, which is why so many series in the franchise (including the ones most grounded in some semblance of mechanical and military knowledge) end up centering around either love stories or a troupe of unusually handsome young men.

That was half the equation; the other half being the transition from toy-based to model-based merchandising, as you said, which drew back in the male fans.