One side isn't bidding at all. They certainly could if they wanted to, but long term is it worth it for them. Thanks the calculation.Getting out-bidded is a part of business and competition, no matter how many times Valve fans try to use this talking point.
epic is probably fine with an ultimately tiny store with only a relatively few major releases on it, that is not the platform Steam has cultivated and by getting into the business of choosing winners and losers by trying to buy large titles exclusivity that's probably not a road that it's worth it for them to go down.