The "stock market companies" is a fantasy promoted by random people, not SpaceX.
What SpaceX shared is that they plan to be "fiber cable" except via space. They'll carry a backbone traffic e.g. between Australia and U.S. via laser links.
Companies that currently pay for undersea fiber cable to carry traffic will pay Starlink for the same service.
High frequency traders would look into this, but I don't think it would be a big revenue stream for SpaceX.
I used to work for a company doing microwave backhaul and they liked us as the speed of light through air is faster than fiber, and they could get more direct links. It was important enough that we had special low latency builds of our firmware with some features removed.
What SpaceX shared is that they plan to be "fiber cable" except via space. They'll carry a backbone traffic e.g. between Australia and U.S. via laser links.
Companies that currently pay for undersea fiber cable to carry traffic will pay Starlink for the same service.
Also, a backhaul for 5G operators (see https://www.telecompetitor.com/starlink-update-musk-sees-mob..., https://www.zdnet.com/article/japanese-telco-kddi-to-use-spa...).
Also airlines.