They do not cast the films, rather they hire casting directors who sort through the thousands of submissions (see above). (moviecastingcall.org)
As happens so often with ensemble cast films it seems they try to supplement the lack of plot with the number of big names they can fit into the credits. (rottentomatoes.com)
Then again, an actual script could have done wonders, as well as a little sensibility when casting the film. (bullzeye.com)