Because investment bankers are just salespeople? Nobody is suggesting AI will replace salespeople in the near future. I could see there being fewer grunt analysts in the future, though.
They aren't? Because I see this happening all the time. Automated checkout lines, E-Trade and online brokerages, etc. Low-value transactions are handled more and more by electronic "salespeople". All it takes to reach high-value transactions as well is for the clientele to decide they trust machines more than humans, which is not all that unlikely given the many sources of human error involved.
It's possible that humans will be involved in high-value transactions like investment for a long time, since the marginal cost of human labor is low as the numbers get bigger, but it's not impossible to replace; we already have the technology.
The examples you give are indeed places where buying or selling happens, but where does the incentive to do these transactions come from? It's still from humans. Sure, we are bombarded left and right with ads that were carefully targeted for us by complex algorithms, but I don't think I've ever bought anything from Amazon without reading a review about the product from another user, or bought stock without going through several opinions written by more-or-less respected analysts.
There is a line (few hundreds k) where it's enough to play but not enough to pay for the costs of a human to help you (sales people/financial advisor/trader type).
Huh? For one, investment bankers are "just salespeople" in the same way doctors are just nurses.
Second, everybody and their mother is suggesting AI will replace retail level salespeople in the future. In fact lots of places, from British supermarkerts (where you can bill and pay for your purchases yourself), to Amazon's Go experiment, and numerous other uses of automation in retail.
Many more lower-end stores did too, pre- or earlier in Amazon's and online shopping's proliferation. It's already happened to a not insignificant extent.
Bookstores is probably a famous example, where the people working there were far more than cashiers, but they still got decimated by Amazon and co.