Thats because Reya Dawnbringer, in addition to a not too shabby 4/6 Power and Toughness (though you may be expecting more for such an expensive card), can bring one creature per turn back from your graveyard, returning it straight to your battlefield
Some have even developed elaborate theories about how the games lore might evolve, drawing on clues from the existing cards and official announcements
That means they get to stick around, you double any enter the battlefield triggers, and sometimes you just get a very large and terrifying army very quickly
Red is meant to be a proactive color, but the problem is that making waves is heavily discouraged in a format with three opponents
In fact, while you get to look at three, after casting it you have the same number of cards in your hand as before