If the Crystals come from space that means it's not a renewable resource nor is it natural to earth, so the volume can't increase, because it's not a living thing that can reproduce. 

What technology did the government have to detect Crystals that they were able to round most of them up? If your average joe can hide it in their kitchen, then realistically there would be more than a few.  Anyone with money or anyone that scavenges for them could have a collection in their house. It could be illegal to have, but laws don't stop people from committing crimes, and the government can't search property without probable cause and a warrant.

Are the increase of Crystals in the world due to black market dealing and experiments with chimerization? If that's the case what's the purpose of dropping Crystals in random places for anyone to find? Rare resources are expensive. Chimerization is 1 in a million, but complete chimerization is even rarer than that. So what's the chance of 1 chimera popping up in a destroyed LA? What makes a complete transformation work in one organism that doesn't work in others, because most die before it's completed.