I guess it's 'pick games that translate well to a movie instead of picking games that have a really strong brand'.

Zelda has been a strong brand for decades but it doesn't lend itself to the screen. There are little to no personalities among the characters. The game consists of exploration, puzzle solving and collecting.

I think Blizzard made this mistake when they chose to adapt Warcraft instead of Diablo. Diablo translates to a linear story so much better.