When you buy from Taco Bell, you’re also buying a product made by a farming company, but you’re not buying from that farm.
Same with EGS/UE. People are happy to buy an Epic Games product, but they won’t buy it from EG, because their store is shit.
There aren’t that many comparable situations where a company both makes a product and has a storefront, without that product being exclusive to that storefront. Perhaps buying Honda, but only used, never from a dealership?