Fractional reserve theft.

First they deceive you, claiming Bitcoin is not secure and that you need them to secure it for you, their offering, an ETF, which is fake paper Bitcoin, just like fake paper gold, or fake paper houses. Commodities that doesn't exist basically which they can print more of out of thin air.

The idea is simple, you buy their ETF, they take your money and stock up on real Bitcoins, then eventually when the price corrects, goes down a bit and people want to exchange for fiat there's not enough reserves to sell. You're now holding a worthless ETF while they hold a large amount of bitcoins, prices may be down for now but will eventually recover.

ETF's allow them to suppress the price and prevent it from rising, just like they do with gold. A pump and dump on the other hand would involve them buying up commodities then sell it all at once to crash the price, they used to do that before but people are smart enough to hold right now.