If one of the manufacturers sold direct cheaper than their distributors----
Natchez, Midway, and others wouldn't bother stocking their stuff.
They'd be left with spending just as much time selling one order for a few things as they did when a distributor
called up and said, "We need 300 of this, 250 of those, 25 each of these".
Some manufacturers won't sell direct at all.
(Try to buy a car direct from any automaker without being referred to a dealer)
Others do at a full retail price for those that can't or won't find it anywhere else.
Then, the retail public can be served without making companies that buy hundreds of thousands dollars from them a year mad.