> I just have a hard time understanding how it is any different than brick and mortar companies using their sales data to determine which products they should have a store brand version of. Costco, Walmart, Target, etc. all do this, and have been doing it for decades.

The legal difference underlying the lawsuit between this behavior by Amazon and the behavior you raise by those stores is not the behavior, but its context.

Amazon, the complaint alleges, has durable monopolies in two relevant markets which the behavior leverages and reinforces, making it a means of illegally maintaining a monopoly.

The other stores do not have monopolies, so the behavior is not part of a system of illegally maintaining a monopoly.

This is very similar to the kind of discussion that happened at the time of the Microsoft antitrusts suit about bundling software: one of the ways Microsoft illegally leveraged their Windows monopoly – in this case to monopolize other markets rather than to maintain the Windows monopoly, but same kind of issue – was bundling IE with Windows. People made all kinds of “well, how is this different than maker A bundling software X with software Y”, and mostly it wasn’t, except that maker A didn’t have and thus wasn’t leveraging a monopoly in the market of software X, so them bundling software Y with it wasn’t an issue.