Fiat is a one trick pony. Since there can be unlimited amounts of fiat printed, every asset that is scarce by nature can have its value coopted by fiat as long as there is a paper market created against it.

Everyone notices this, silver bugs, gold bugs, even the GME apes. However, Bitcoin has a trick up it's sleeve that these other assets don't.

Fiat entities against the scarce asset, be it shares, precious metals, Bitcoin, etc may try to drive the price down by selling futures contracts heavily and at a loss. A cash setted ETF is ideal since liquidation would only result in cash collateral loss, and no need to buy spot to cover which may result in cascading liquidations, or a squeeze, as with a spot ETF.

Essentially selling paper contracts at a loss drives price down by enticing owners of actual assets to buy the lower futures contract and selling thier spot to pocket the difference. Eg. A Bitcoin trader buys a 49k futures contract for 1 bitcoin and sells 1 bitcoin for $50,000, so he nets $1,000, FOR FREE, and the selling pressure also drives the spot price of bitcoin down.

Where did the $1,000 profit come from? Whose money is that? Whoever was “silly” enough to sell the futures contract for too cheap. But were they silly? Not if they were someone who could print fiat money in unlimited quantities and wanted to drive down the price.

Bitcoin is unique in the sense that physical delivery is trivial to take, and easy to secure and hold. At some point if actual bitcoin is what will be demanded and accumulated long term – not paper promises for it, backwardation will occur in the futures market, since primary cause of backwardation in the futures market is a shortage of the commodity in the spot market. Normally when this happens new suppliers come online and ramp up production. Bitcoin differs from every single other asset in that this is not possible supply is fixed and cannot be increased

This is why Bitcoin is inevitable. This is why energy FUD. This is why trying to change protocol to PoS. Price manipulation can only be temporary, unlike with other commodities where supply can be increased to meet spot demand, so other avenues to weaken it must be found.

Make no mistake, Bitcoin is under attack and it will always be under attack. PoW is the defence mechanism that keeps the manipulation at bay.

https://bitcoinmagazine.com/markets/bitcoin-futures-market-explained-price-manipulation

"The CFTC staff handled it strictly on procedural grounds, but at the leadership level I communicated with Treasury Secretary [Steven] Mnuchin and NEC Director Gary Cohn, and we believed that, should bitcoin futures go forward, it would allow institutional money to bring discipline to the value of the cash market," Giancarlo told CoinDesk. "And that's exactly what happened."

https://www.coindesk.com/markets/2019/10/22/trump-administration-popped-2017-bitcoin-bubble-ex-cftc-chair-says