The Italian sprinter, winner of omnium gold in the 2016 Rio de Janeiro Olympic Games and Sunday's Cyclassics Hamburg, broke his contract to leave Sky after three years. He announced the deal with Belgian team Quick-Step Floors this week.
"I had three great years with Team Sky and I was not going to just change to any team, it had to be a quality team," the 28-year-old from Verona told Cycling Weekly.
"Sky was fundamental in my nine wins two years ago and my wins last year, but I did not want to have another year like 2017 where I cannot have the opportunity to reach the goals that I have.
"It was difficult to leave Team Sky because it's one of the best teams in the world but Quick-Step is an ideal team for sprinters and it was an opportunity not to be missed."
Viviani, winner of the 2015 Giro d'Italia stage in Genoa, had a contract that ran through the 2018 season.
He considered a mid-season move with UAE Team Emirates but the opportunity he wanted came when Marcel Kittel announced he would leave Quick-Step for Katusha in 2018.
The door opened for Viviani to join Patrick Lefevere's team, which also has Colombian sprint star Fernando Gaviria.
"Missing the 100th Giro as the Olympic champion was not the whole problem, it was more looking ahead to the next year. I didn't want to have another season like 2017. Next year I want to be able to do the Giro and various other races but team Sky can't get give guarantee," he added.
Watch: Elia Viviani's toughest day
"I had this chance with Quick-Step and I had to take it. Sky has the men to lead out sprints, but their focus is on helping the classification leader.
"It all happened within the last week when Marcel Kittel announced he was going to Katusha and team Quick-Step was searching for a sprinter. It's true that Fernando is still there but Fabio Sabatini is staying and they have many men to help with the sprint.
"Patrick Lefevere has always had two sprinters. For sure Fernando, after four stages in the Giro, will want to race the Tour de France. If he does then there will be space for me in the Giro and the Vuelta and other races.
A rider normally must pay a fee when he ends a contract early. Viviani's agent Giovanni Lombardi, however, worked with David Brailsford and Sky agreed to let Viviani go without any fuss.
"It was difficult to go away from Team Sky because it's one of the best teams in the world but Quick-Step is an ideal team for sprinters and it was an opportunity not to be missed.
"I need to thank Team Sky for understanding and give them this opportunity. David Brailsford understood I could not achieve my ambitions in Team Sky."
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