The reason this is ahead of the other symmetrical draw spells is that it either generates you mana or costs none once it has resolved thus allowing you first dibs on using the new cards and no disparity in mana
Allowed sets : Alpha, Beta, Arabian Nights, Antiquities, Legends, The Dark, Fallen Empires, Harper Prism Book Promos, Ice Age, Homelands, Alliances, Mirage, Visions, Weatherlight, Portal, Tempest, Stronghold, Exodus, Portal Second Age, Urzas Saga, Urzas Legacy, Urzas Destiny, Portal Three Kingdoms, Starter 1999, Mercadian Masques, Nemesis, Prophecy, Invasion, Planeshift, Apocalypse, Odyssey, Torment, Judgment, Onslaught, Legions, and Scourge
There are 5 different Jungle pack variants, with obviously the short packs being the most scarce
This increased supply made the game more accessible to a broader audience