Unreal only has a 5% fee on games that made over 1 million USD
Unity wanted to add a 0.20 USD tax for every download after you made 200K USD 200K users(which changes depending on how many downloads your game has and which plan you are using)
Units pricing method could have been easily exploited, game developers would have to pay for people pirating their games, if a free to play game reached those requirments, it could cost them more than the game made, giveaways would cost game developers money and all unity games would have to collect data