While the scripting may be easy to learn, controlling the engine is very difficult.
Hunting down bugs in a nearly completed game is 1001 nightmares as there is very little debug help...
Only strict coding discipline can help here, but to get to that point it takes years of working with the engine in order to understand how to avoid the neckbreakers.

E.g. at AckCon we are doing Acknex projects since several years, and still have problems piling up close to release stage. There are so many pitfalls, and so many of them only get visible after a long time of experience with the engine.