Sorry, but you're conflating "using" cash with "having" cash. I can't speak to the rest of the world, but in the United States, the 4th amendment of the Bill of Rights states that you're to be free of unreasonable search and seizure. You can have any amount of money on your person for any reason you like, so long as you don't do something illegal with it. These cops are stealing cash under the pretense that it could have been used for something illegal, which directly conflicts with the idea of being innocent until proven guilty. The sham they perpetrate is that it's the cash being accused, not the person. It's bullshit and they have no intention of doing anything other than keeping the cash.

Want to withdraw all of your cash in dollar bills so that you can lay on it like a mattress? Legal, and cops shouldn't have any claim to it.

Want to withdraw all of your cash in golden dollar coins and try to swim in it like Scrooge McDuck? An ill-advised plan, considering how fucked the American healthcare system works, but legal, and once again, cops should have no claim to it.

Just having property - cash, gold, diamonds, very small unicorn figurines, whatever - is not an illegal or even inherently suspicious act.

Without probable cause, there's no reason a government agent should ever be able to take any property from you.