Earlier quoted context omitted.
I know it sounds silly but it’s legit. Tons of stories of people driving out to buy a car, getting pulled over, having $10k seized without being charged with a crime, and then having to sue to get it back under a presumption of guilt. Bitcoin is harder to seize under civil asset forfeiture. ETA: in the US. Not sure about other countries.
Or they could have just used a bank account. More people have lost money to Bitcoin scams and exchange fraud (see e.g. Mt Gox) than have lost their money to civil forfeiture. Depending on the price of Bitcoin, but (based on the current price of Bitcoin) more $$$ has been lost to crypto fraud as well.
One reason is that banks will refuse to open an account for people whose records show past behavior they don't like (bouncing checks, overdrawing accounts, leaving fees unpaid, etc.).
Some other people could open a bank account but have practical reasons not to. For example, identity theft. Someone drained all your accounts, but you still have a good-paying job. If you open another account, maybe they will drain that one too? Maybe not a good risk to take when you're trying to stabilize your situation.
Another example, probably more common, is poor people who have court judgments against them from people they owe money to. You have medical debt, or you got evicted and owe back rent, or you messed up withholding and you owe the IRS back taxes. You might be living so close to the brink that your monthly income is $1500 and you need $1499 to survive. The court lets the creditor garnish money from your account, so one day you check the balance and find $500 gone, and you can't pay your rent or buy gas to drive to work. So you prevent that scenario by dealing entirely in cash and not opening an account.