Because Dungeon World is about telling compelling stories about cool characters caught up in awesome events. 5E is about grinding out levels and amassing magic items.
In all seriousness, these games are paradigmatically different. 5E has a lot of crunch, there are rules for everything, and combat takes half of forever, especially as power levels increase. The game has a lot of minutia which can also slow down play. And it preserves the old-school progression curves where after about 7th-9th level, there's no reason NOT to play a wizard.
Dungeon World is all about the story. While it keeps (IMO) too much of the cruft of D&D to really shine like its parent (AW), it cleaves to its theme pretty well and is still a story-based game at its heart. Play will proceed quickly and the game will focus more on who the characters are rather than what the characters have.
It's also infinitely cheaper.