It’s not for some random reason. Up until today, HDRI images were used mainly for baking light and reflectiosn in videogames. That’s the reason of compression quality and aggressivness, since HDRs are usually heavy images. Straight up config from UE is not for thought for high end image rendering as ArchViz requires. UE4 is a Game Engine after all. But it’s a great one and allows it to be used for cinematics also with just a few tweaks around.
If you don’t want your texture to compress make sure you select the option in the texture edit tab and also change it to never stream.