Epic takes a 12% cut, as opposed to Steam's (initially, it lowers once it hits certain revenue thresholds) 30%. As well as that, the usual 5% cut Epic takes from games using UE4 doesn't apply to games present on the EGS. In addition, Epic is (currently) offering financial security. They don't offer developers a lump sum to delay Steam/GoG releases, but rather a minimum sales guarantee. If the game doesn't reach a certain number of sales, Epic is willing to pay the difference. The amount is something that depends on the scale of the game, so there's no concrete numbers floating around which point to how much Obsidian/Private Division were guaranteed in exchange for exclusivity.
What Epic is currently offering is tough to pass up, but you'd have to be foolish to think this is a sustainable way to run a platform. If the EGS catches on and the competition shrivels up, these bonuses are going to disappear and people are going to witness what a real PC monopoly looks like.