They didn't have minimum quantity orders, it's actually the opposite.
GW removed the quota for boxes they had during the pandemic for Dominion and let FLGS order as many as they wanted, so they ordered a lot of them, but not really more than they needed, maybe just a little more.
The issue is GW first delivered only a few boxes to each store, and they did sell out immediately, while GW kept selling Dominion through their stores and online store. So when the rest of the boxes got delivered to the FLGS a couple months later, all their clients already bought Dominion through GW and there was no demand for it anymore.
That's why most FLGS stores still have Dominion boxes to this day...