Why didn't lego make puple ussal crabs?It wou be cool if a Master builder set 2 came out with a puple ussal.

Well, seeing as how the majority of the MasterBuilder pieces were red, orange and grey...

No, I think that explains it.
I think Purple Dave of Mod made a Purple Ussal.

well since the master builder set only really has the olors red,orange and grey they had to use those colors.but if your want to make a purple ussal crab just paint some of the pieces purple

The Master Builder would have costed more if they included extra purple parts. And they couldn't just change the color of some parts or other animals would have been un-color coordinated. But you can make you're own purple Ussal Crab if you have the right pieces to build it.