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Sagan is the only cyclist in history to have won 3 consecutive world championships in the road race. Winning the road race worlds means wearing the iconic rainbow stripe jersey for the next year, and comes with an incredible amount of attention. He sort of exponentially grew his fame by winning again and again in the rainbow jersey. That in addition to his huge list of accomplishments, including 7 green jerseys by riding on his all-around capabilities.
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You may notice there are 22 teams, but only a handful of GC contenders. Some teams are built to compete for the yellow jersey, some for green, some for stage wins via sprint, some for stage wins via breakaways, etc. Bora Hansgrohe built their team around Sagan and his bid for an 8th green jersey.
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Points are awarded for placing in intermediate sprints during the course of each stage and for top finishers at the end of the stage.
I hope some of that helps!