The problem isn't that it's too hard to organize; it's actually quite possible to organize and direct a feature length film as long as you spend enough time on doing it. The more fundamental and underlying problem is that most individual brickfilmers are pretty unorganized and don't take orders well at all. This is what I found out when I tried doing a community project with around 10 animators. All of them were enthusiastic in the first week, but as soon was I tried to get some work done with them over half of the animators never returned any of my messages, emails etcetera.

So yes, it's a pretty impossible feat to pull off but it's not necessarily because of a lack of motivation from the director's side.