Not to mention time.
Okay. Lego obviously needs to create new character designs. All they need are:
- A computer
- A fancy 3D Modeling program
- A Jar of Peanut Butter
Don't forget the most important thing:
Money to pay a employee skilled in 3D drawning.
Generally, something people forget is that when a company is cutting corners, it is not an "if/if not" situation but rather an "either/or" situation. So for instance, using character models that already exist for minor characters or characters who only appear briefly isn't done because the filmmakers are lazy, but rather because rendering more major characters and scenes takes precedence and sacrifices have to be made to allow that. If you only have the time or budget to design, render, and rig a certain number of new character models, then you're going to spend that time on the most important or most prominent characters, not on characters who only appear in the shadows for a few brief moments or who appear only as crowd-filler.
The BIONICLE movies were just as egregious about this. Remember "Kongu" in Legends of Metru Nui[/i}? He was just a palette-swapped Hafu. In fact, all background Matoran had only subtle differences, and already-rendered assets were frequently recombined into new character designs (example: The drones in Vakama's forge in Legends of Metru Nui used a combination of Bohrok and Matoran parts rendered for [i]Mask of Light). In LEGO animated features, this kind of cost-cutting decision is to be expected, since one of the key features of LEGO is the ability to combine parts in new combinations to create new models.