The claim could be something related to interfering with their business.

"GOOG agreed to provide my company a service that we have reasonably relied on"..."GOOG struck my app for no cause causing my business damage..." and so on.

Though, in-real-life, people who use google services have probably agreed to terms to bar any such claim.

In many countries a ToS is not legally binding, as its not considered a legal contract.

...but its entirely legal (and reasonable) for a business to stop doing business with an entity simply because they feel like it. No matter if they entity was relying on the service or not. It happens all the time.

Except contracts may state otherwise and a court might decide that the "I no longer want to do business" clause is invalid or not applicable. And except in my countries you certainly can't just stop doing business with someone, including a few European ones. Double if the other end is a private customer.

I'm not a lawyer, but it feels like an abuse of monopoly power (Antitrust laws)

Google sounds like they are using their control of the Android store to prevent an application being published that competes with their Google Maps Mobile App, which also offers similar public transport tracking and time-table information

I think you'd need to show some evidence that public transport apps (or apps competing with Google's, in general) are particularly targeted.