The adherence to a Faction War.
WarCraft: Orcs vs Humans (year 592 Kings Calendar)
WarCraft II (4-8 years later in Azeroth)
WarCraft III (20-24 years later in Azeroth)
World of Warcraft 2004 ( 25 years later in Azeroth)
WOW: TBC ( 26 years later in Azeroth)
WOW: WotLK ( 27 years later in Azeroth)
WOW: Cat (28-29 years later in Azeroth)
WOW: MOP ( 30 Years later in Azeroth) -Faction war should have ended here.
WOW: WOD (31 years later in Azeroth)
WOW: Legion ( 32 years later in Azeroth)
WOW: BFA ( 33 years later in Azeroth)
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And that is the thing that keeps me playing WOW, no F2P B2W mechanics, aka Loot Boxes. I can't play games with loot boxes. I spend too much money playing them.