Do people have any concept of how the law works.
Oh they only seized this amount, or that amount. They didn't get XYZ.
When they make a initial raid / seizure, they only get what is initially available.
Once they have been arrested, then they can do a lot more digging and apply more more seizures. They can also start applying for "profits of crime" seizures
Think of it of "we pulled you over for a broken tail light" scenario. They find several bags of weed. This then gives them the right to go for a search of a house. They find more weed, a bundle of cash and several mobile phones. So they seize the phones and then then can go after the contacts....and on and on.
So in this case the initial seizures and arrests are a way to gather more evidence and go for bigger rewards.