First was most likely the idea of having a modular corvette chassis that could be retrofitted to different tasks, and serve as light transports (like the unarmed Ambassador version), workers, and weapons platforms. Then a few of those chassis were built and stored aboard the Mothership and Scaffold. The Porter was first conveived as a deep space cargo tug, then retrofitted with whatever magictech they use to make them actual capture vettes, then the repair corvette as mobile refueling point for exploratory craft, and later the Hammer was developed with anti-strike turrets in place. Because they already had the necessary spare parts lying around, they could churn out heavy vettes and later multiguns as the need arises.
Inspiring new designs is a plus, too.