Cars 2 wasn't that bad of a film. Did it do as well as the first Cars, eh no but I still thought it was pretty good. I haven't seen Cars 3 but like most sequels, it will never match the mustard of the original.
The original movie Frozen was going to have a completely different story, much less outcome until they heard the main score that has basically got a stranglehold on the top spot for Princess movie songs. Even the main scores from Littler Mermaid, Aladdin or my mother's personal favorite Beauty and the Beast(she didn't like the live action remake as much) can't match the popularity that Let it Go now enjoys. The score was so good that they completely re-did the movie from practically scratch. Plus, lets not forget that Disney does not make the mistake of 20th Century Fox by giving away merchandising rights to an unknown director for a movie that ultimately became a cult in Star Wars so cashing in on Frozen in every capacity is a given. They're still doing so five years later and a Broadway Musical is slated to debut next year(honestly I'm surprised it took this long). If the musical is a hit, it will basically be free advertising for the sequel movie and the build-up for it will be enormous(I wouldn't be surprised if they spend like 100 million on Advertising). If the movie gets raving reviews, I'm telling you that 1 Billion is a given and 2 Billion is not out of the realm of possibility.