That's not true. The price would reflect it. Suppression. Easy to dump and scare the market. Scoop up coins at the bottom and reduce fractional reserves. Rinse and repeat.
That's how Binance has done it. And that's his BlackRock will do it.
Discussion
so your theory is they will rehypothecate, and then dump the market with bitcoin they don't actually have because they rehypothecated it, and then somehow buy back all the bitcoin they have rehypothecated and also the bitcoin they sold all because they "panicked" the market?
Not how bitcoin works.
I always find it amusing when people imagine that the most bullish asset in human history is having it's price suppressed. Boggles the mind.