The Belgian ended his 11-year stint at the club this summer to join Anderlecht as player-coach.
The 33-year-old defender, who is preparing for a star-studded testimonial at City, told Sky Sports: "I could have ended up at another club, and out of four league titles you could have maybe turned it into eight, depending on which club you go to, and how successful it is.
"It's a competitive club, City. It's not like you can sit down for a year and wait around for what happens.
"Every transfer window, every six months, you are competing with the rest of the world. Anyone better in the world, they have the responsibility to get to improve the team, and so nobody gives you the gift of staying at City for 11 years, you have to earn it for 11 years.
"Doing this, while being impeded by your body, my mother would have been proud of me."