From GameWatcher: “Borderlands 3 is coming out very soon, on 13th of September, and though fans expected for the game to allow for preloading via the Epic Games Store, which it will be exclusive to, it seems no such thing will happen after all.
Tim Sweeney just confirmed that Epic won’t be able to deploy the preloading feature by mid-September, and that players shouldn’t expect for the option to be available in time for them to preload Borderlands 3.”
Source: N4G PC Epic Games Store Preloading not ready in time For Borderlands 3