I am just a forum moderator and don’t work for epic but I know that epic’s legal team take piracy of assets and the engine very seriously and will take the appropriate action.
I know it can be discouraging but to be honest it happens to pretty much all online marketplaces as there is no real way to stop it, although there is no need to be discouraged as the people buying pirated assets cant release a game that contains pirated assets in most of the major markets(which means they wont be able to make even a fraction of the money they could using legit assets), for example if I bought a pirated pack built a game using that pack and tried putting on something like steam epic’s legal team could have it taken down(maybe additional legal action as well) so the only way I could release the game would be to get the pack from the official marketplace so the creator would still get the money.