production - Why are certain scripts produced as animated features instead of live-action?

To answer specifically to your case of Tangled, Disney has a long tradition of blockbuster animated musical fairytales, and it's a business model that works.

Their most recent live-action exception, Enchanted (2007) did pretty well at the box office. It didn't perform as well as animated movies aimed at the same audience though, and was beat out by Shrek the Third and Ratatouille (and also Alvin and the Chipmunks, which kind of throws a wrench in my theory, but I'm forging ahead anyway). Tangled pulled in over 200 million more than Enchanted, which seems to show that animated movies, particularly animated princess movies, do better than live-action ones.

Merchandising is also always a major concern for Disney, and it is harder to make palatable merchandising out of live-action images. Dolls, t-shirts, etc., especially modeled for kids, look a lot better with images that were meant to be 2D. (that is opinion-based, not fact)

What is fact, though, is that live-action films cause major licensing problems for Disney.

This requires a detour into the history of the Disney Princess merchandise line. Since its introduction "Sales at Disney Consumer Products rose from $300 million in 2001 to $3 billion in 2006. Today there are over 25,000 products based on the franchise". In recent years, the line-up has been exploding to provide more products and revenue, and it's gone from 8 characters to 13 since 2009. That's a princess a year, a big jump from the earlier rate of a little less than a princess a decade (starting from 1937 with the production of Snow White). This shows a desire from Disney to increase revenue by introducing more Princess characters.

Live-action princesses are harder to include in this merchandising boom though. From an article on the phenomenon in the Wall Street Journal, Disney abandoned the plan to add Giselle to the princess line-up "when it realized securing the life-long rights to the image of Amy Adams, who plays Giselle, was harder than an ugly step-sister squeezing into Cinderella's glass shoe."

So, in sum, Disney chooses to animate fairy tale movies because it lets them make more money, both in the box office and over the long term.