You must have misunderstood the news article. It didn't say they will buy what's left of FTX but they will buy or invest in cryptocurrencies because the prices are down as a result of the FTX implosion. These banks are business opportunists at the end of the day and will take a calculated risk if a chance presents itself.
That's right. They risk with the investment in Bitcoin and speculate just like everyone else on profits. They do the same with the "normal" currencies. With cryptocurrencies, the risk is only much higher. You can also call it an additional asset class. Investing in currencies, bitcoin, gold, real estate, cars and more is just a way to invest your money and not let it destroy by inflation. If possible with the smallest risk.
I mean it is super smart to get in right now. They could build a billion dollar portfolio and make as much as 50 to 100 million dollars just from staking it, and then they could also make more from the amazing increase that we are going to have soon enough as well.
I know not many people could do such a thing because they do not trust bitcoin with a billion dollars but Goldman Sachs is rich enough that if their 1 billion dollars becomes zero, they would still continue operating without any problems, this comes with the issue that if they turn 1 billion into 2 billion it won't really be a big profit neither, but it's worth trying at least.