"Why would you want to pay the reseller as well"
Excellent question and one that requires an answer from a "reseller's" point of view. But first, there's one very important fact which must be established. The size of the model submarine community is incredibly small. Read that as "there ain't too many guys to sell to". Carry that a step further - this isn't the business to get into if you're looking to retire early.
So an honest answer would be "to allow that reseller to stay in business". Without spending a whole lot of time and bandwidth on a long drawn out description, look at it this way. If that "reseller" has an item in stock that you desire, chances are that he has several others, as well. Generally, if he buys one of an item, he'll get a discount, but if he buys say 5 or 10 of that item, he'll get a better discount. But now he has a substantial investment sitting on his shelf. If that item was imported from the other side of the ocean, he's gone through the hassle of importing, paying taxes, duties, shipping, etc. which generally means that the buyer doesn't have to. OK, you say, "but so and so (the manufacturer) sells that for $100 in Europe and so and so (the "reseller") here in the states sells it for $120. I'll buy it direct from the manufacturer in Europe". Besides the convienence of getting it from the "reseller" (it's sitting on his shelf, you'll almost certainly get it quicker) the hassle with importing it has already been done.
From the "reseller's" point of view, he might have purchased that item at a 25% discount which could be seen as a $35 profit. But don't forget that he also jumped through the hoops in getting that item to his location and tied up a lot of his money just to have that item sit on his shelf. Truth be known, if it sits there long enough, he probably would have made more of a profit if he had put that money in a money market account. And, if that's the case, he probably wouldn't stay in business so those other items you get from him that you can't get anyplace else wouldn't be available any more. Case in point: I've sold literally thousands of stuffing boxes and linkage seals in the past 11 years. But even if I had sold all of those within just the past 12 months, and nothing else, I wouldn't be in business any more.
And yes, it helps the manufacturer, too. True, he sold that item to the "reseller" for less than what the end user would have paid but he sold several of them to the same buyer at the same time which means that his cash flow was up. And that goes a long way toward paying for what he has to stock to be able to manufacture that item.
The U.S. of A - Land of the Free BECAUSE of the Brave