Large opening orders, and reorders is used as a means to exclude other brands from competing.
If a shop has to invest $10-40K in a particular brand / line of goods, and needs to generate $XX dollars to be able to reorder they have a huge disincentive to offer any other brand.
Few LDS can afford to carry multiple lines of competitive products.
Lets say you want to open a dive shop. You need to be able offer regulators, BC's exposure suits, masks, fins, instruments and tanks.
It helps if you can offer a name brand regulator, but to be able to do so the regulator company will require (via opening order requirements) that you also carry their BC's and Instruments, exposure suits etc.
Once you pony up there are scant few dollars left in the "open to buy budget" to stock other BC's, or other Instruments, particularly if these "others" also demand a large opening order.
Some will argue that's done to ensure the customer has access to the complete line offered by a given brand, and that the store staff be familiar with the entire line. Maybe, but the real reason is to limit competition.
Tobin