Those manufacturers really depend on their retail partnerships. Sure, if they want to sell all their 3080 and 3090 boards direct with a queue, and abandon retailers, they could do that. But then Newegg and other retailers would be like “Oh, you gonna play us like that? Ok, guess we’re not going to stock any more of your shit.” And now EVGA’s direct store becomes the only place to buy EVGA stuff.
If that happens, sure, some brand loyalists will go to them direclty. When a new hot product comes out, people will still go to them directly. But for most of their product line, like power supplies and all the other video cards that aren’t 30XX, people are going to be building their computers on Newegg. And if EVGA products aren’t listed there, customers are going to go with a different brand.
If it was in their best interest to go direct and avoid middle-men, retailers wouldn’t even exist and every manufacturer would just be selling direct.