The former Brazil international agreed a mutual termination of his Milan contract on Monday before Orlando announced Kaka as their first designated player - someone who can be paid outside the salary cap - a day later.
Following the end of his second stint at Milan, which was sandwiched by a four-year stay at Real Madrid, Kaka will feature for Orlando in their maiden MLS campaign next year.
Prior to that he will return to first club Sao Paulo on loan to maintain fitness, with the 32-year-old stating his desire to join Orlando was not completely financially motivated.
Instead, he spoke on Wednesday of his desire to help the sport continue to grow in the United States, explaining that he turned down more lucrative offers to play elsewhere.
"At the end of last season, I started to think about my future and whether I would go back to play in Brazil, [play in] the USA or stay at Milan," he explained.
"It was difficult to leave Milan [but] my expectation is that soccer is going to become the number one sport in the USA.
"They pay me good [money] but I had another opportunity to earn more money. I always think about the project.
"I stayed in Milan for six years, I stayed in Madrid for four years, I played in Brazil for nine years so I always think about the good projects.
"They pay me good money but I could earn more elsewhere."
Kaka is the second high-profile signing made by a soon-to-be MLS club in recent weeks, with Spain's leading goalscorer David Villa becoming New York City's first signing last month.
The Brazilian playmaker, who won league titles in Spain and Italy as well as the UEFA Champions League and the FIFA World Cup, revealed he discussed the merits of his move with former Milan team-mate David Beckham - the first global star to make the switch to the MLS with LA Galaxy.
"I think it is the right moment because I'm not too young but I'm not too old. I can still bring a lot to the league, which is getting better," he added.
"I can say I'm studying the league. My brother [Digao] played here and David [Beckham] played. I spoke to him a lot.
"When I start to play, I'll figure out how I can improve the team."
