Who said anything about starting over, like I mentioned they could have dropped the Tron theme and kept everything else the same, calling it something different and still kept their investment and opening date. Think about it, besides the ride vehicles looking like Lightcycles, what is there that is really Tron? Not much, which by the way is one of the complaints on sites like this about the ride.
But they wanted to kept the Tron theme even after the movie underperformed. Because despite the movie box office Tron is actually a legacy franchise that ties back to Disney, so its got the nostalgia factor. And by all accounts its popular.
Again its only on sites like this that anyone actually cares that its tied to an franchise that didn't do well at the box office. To the public, they like to ride in the Grid.