But they can. That's why they got into legal trouble with the SEC. See page 4 on the actual SEC document on the case, the section called "Best Execution": htt

But they can. That's why they got into legal trouble with the SEC. See page 4 on the actual SEC document on the case, the section called "Best Execution": https://www.sec.gov/litigation/admin/2020/33-10906.pdf https://www.sec.gov/litigation/admin/2020/33-10906.pdf