HN title is significantly different than the question the submission actually asks which is "why do TRADERS in investment banks . . . " and should be updated
The job is actually extremely complicated. I wear many hats daily including working as a software developer, IT project manager/architect, salesman to clients, point of contact to other institutions trading desks, legal drafter, tax/accounting policy design, deal negotiator, risk taker/manager, systematic/fundamental strategy research etc. My job title is "Trader". There aren't any dumb big swinging dick 80/90's style traders left shouting buy and sell (if they are it's purely relationships and at small shops). Nearly everyone on my desk has a CS degree or similar quant background.
AI/deep learning is currently nowhere near being able to master one of these fields let alone cohesively manage all together in a direction to actually make money (just pay a "trader" a 200k-1.5mn USD a year its much easier). Most grunt work is automated and most outfits do in fact make use of statistical methods/classifiers/predictors and differentiable networks where appropriate. At the crux of it someone needs to manage, design the systems and fill in for them with a bit of intuition and common sense where there are gaps. The world is a chaotic place and its not getting simpler. Machines are not robust against chaos.