I think the mini cruises are at a price point the average upper middle class family can barely afford. They make more money having two cruises in one week than having one. The short cruises have always been the money makers for them. I assume they are not stupid and are doing what makes them money.
Everyone looks at the discounts and thinks they are struggling, but even with the discounts they are still priced way above the competitors. It's a mind game they play. You think you are getting a deal, but you are not. They win.