Blizzard missed the forest for the trees when they ordered that the Warcraft movie start with the First War. A movie with a budget of hundreds of millions behind it needs to cater to casual audiences, or else they're you're not going to make a profit. Blizzard got too caught up with their years of backstory lore and thought that they needed to start with WC1, when the First War has little appeal to casual audiences. From a casual's perspective, a WC1 movie would just be a retread of the "humans vs invading Orcish armies" story that LotR did (except with 3D CGI and a plot that wasn't written by Tolkien), and would thus be compared unfavorably. The First War isn't even what is unique about Warcraft. WC3 is what was unique about Warcraft. The story of an Orc reforming his society, or a human prince descending into evil and becoming a necromantic overlord would have been far more unique. Plus, the movie would aesthetically be more interesting to audiences.