They don't.

After the Volcker rule the big banks had to close their prop trading groups: https://en.wikipedia.org/wiki/Proprietary_trading

The idea that investment banks are filled with human "traders" is Hollywood nonsense.

Most trading activity (and even filling of retail order flow) is now done by quant-driven funds.

According to LinkedIn there are 573 people with the job title 'trader' at Goldman Sachs. I'm scanning through the list now- titles like Fixed Income Trader, Mortgage Trader, Rates Trader, Oil Trader, Equity Sales Trader, FX Trader, Emerging Markets Trader, Base Metals Trader, Interest Rates Trader, Investment Grade Bond Trader, Equity Derivatives Trader, Commodity Trader.... I found all of these on the first page of results (25 people)

By contrast, about 37,000 people work at Goldman. Those people with the name “trader” in their title are simply executing client trades as a service for fees—-not speculating with the banks own money.

I stand by my point, the idea that Goldman is full of traders in the Hollywood sense is nonsense.

There are not a lot of equity cash traders left in Wall Street firms; but it's not like equity cash is the only thing to trade.

Trump has undone the Volcker rule portion of Dodd-Frank [1], for what it's worth

Goldman Sachs, et al, would not lobby the government to get rid of a law that prevents them from doing something unprofitable.

[1]: https://www.politico.com/story/2019/08/20/volcker-rule-josep...