I'm really curious if this is related to physical retail & first party (Sony/MS) deal terms.
Often, and obviously I have no knowledge of Gearbox/Epic/1stP business ties, but often when you have publishing distribution deals with retailers or platforms, there are "Favored Nation" clauses where if one distributor is given special terms, you (as the retail/platform with said terms) are also to be provided deal equal terms for yourselves. If this is the case, even if Epic is knocking down the price $10, Gearbox/2K would likely be obligated to provide an equal pricing structure for Amazon, Sony, MS, and anywhere else with Favored Nation terms (which is super duper common for distribution deals).
Definitely a bit of a mess. I legit appreciate Epic trying to drive more MAU for their store platform where it matters most to players while not at the publisher/developer expense, but it also kind of seems like they didn't really think through how complicated multi-platform pricing works.