User blog comment:Dava4444/Irrationality in Rapture, or 3 new recipes for sea slug..?/@comment-75.36.143.210-20140324222736

Difficulty One is the significant number of mod tools needed for a old custom modified Unreal Engine (even after Infinite went to Unreal Engine 3 its probably got some customizations on the tools they used). Licensing issues alone are a major problem.

Second - is legal restiction on the assets, which to 'mod' have to be supplied (cant hope for sufficient fans to recreate all the assets from scratch)

Third - Money - the Game client program needs to be significantly modified to take new mod'd  content  (since it wasnt designed for it from the start like other games). The company would be loath to spend money on doing this and pay the expenses for organizing the other two things above.