IMO they are scams, because custody of BTC can never be guaranteed. What if they lose it, suffer a hack or a rogue employee drains the stash? They won't be able to recover it. The government won't be able to bail them out, because they can't print bitcoin. They can print fiat shitcoins and buy BTC with them, but that will increase the price, which will become a runaway train and no amount of money printing will buy the lost coins.

Imagine there was a drought and there is no food in your country, I.e. it's very scarce and therefore expensive. You can print money and give it to people, following the logic that if you give everyone $1m they will be able to buy the expensive food. But they won't, the food prices will go up and soon that $1m won't buy a bag of pasta. Because in a famine it's food people need, not dollars. If there is no food there is no food and no amount of green pieces of paper will make food magically appear. In the case of a bitcoin ETF that lost people's bitcoin it's bitcoin they will need, not dollars.