How did Diet Coke and Mentos become so popular?

Coca-Cola and Diet Coke are two brands obviously from the Coca-Cola corporation. Since 1886, Coca-Cola was a huge hit on the street since it's taste was delicious to a load of people. After a huge franchise success that took years to make and a 124 year ad campaign, Coca-Cola is now a huge hit. Diet Coke was made in the 20th century to have 0 calories, seemingly making it soundhealthy (or just sound healthier than Coca-Cola) making people think "Hey, this will be tasty and better for me to drink!" to add on to a popular soda corporation's reputation as one of the most popular drinks in the world!