The real reason was that Banzu had found the plans in the Old City mostly as-is and hadn't considered building something different. He hadn't told anyone that though, allowing people to assume that he'd come up with the idea on his own. He paused for a moment to think of an accurate response, and settled on a fairly obvious one.

"Got more experience working with metal and machines. Union generates its electricity with machines like this too, so there's more up-to-date reference material than there is for sails."