Is that comparable to the owner of a mall watching who goes in and out of which shops to decide what stores to add to the mall?

> A customer of AWS has a reasonable expectation that the information it keeps on AWS's VMs are confidential.

This is where End User Agreements may be worth checking. There may be a specific clause AWS customers agree to.

Isn't the important factor whether it's trying to become one? Windows and IE were never the only possible options.

One can violate antitrust laws without being a monopoly. Certain parts of the law (regarding collusion on price setting, for example) can be broken by very small businesses.

See this helpful FTC page: https://www.ftc.gov/tips-advice/competition-guidance/guide-a...

As others note you don't need to be a monopoly to violate anti-trust laws. However, as it relates to being defined as a monopoly this ability to leverage your market position to stifle competition is the exact type of behavior that would support a finding of monopoly...most non-monopolies can't leverage their market position to unfairly compete