Isn't this the same case with Safari on iOS devices?
Update: I posted this before the motivation was published.
Basically the way the EU sees it, Google has a monopoly in a market: mobile operating systems. That is, if you're an OEM and you want to sell a device with an operating system, Google is currently the only place you can really turn. Apple exists but since it doesn't sell its operating system, it's not a participant in this market.
So the EU saw Google saying to OEMs "you can have Android but you have to install our stuff on it or pay extra" and decided that Google was using its monopoly position in one market (mobile OS) to give itself an advantage in other markets (app stores, browsers, search). They see this as anti-competitive.
If an OEM sold a phone with a stock AOSP build, I think they'd be fine with calling it "Android" without permission. Google might attempt to enforce their mark anyway, but they wouldn't have much of a case.
If the phone ran a fork like LineageOS, the OEM would need to be more careful about their use of the mark, but I imagine they'd still be okay with language like "Android-based".
Edit: like Netflix, Hulu, and Snapchat
Reducing the choice to just Google phones running Android will spark other providers to develop their own OS and increase competition in the market, which would indeed lead a great deal of people to say "Good job, EU" if the EU was the catalyst for such a scenario.
Google could shut it down and only publish their own phones, but they don't have the chops to become a premier customer goods maker. The field would be free for Apple until Samsung catches up. In the end Google lose negotiation power in getting their search engine, browser and services on Apple's and Samsung phones.
Basically they would be the main loser in the move.
Apple isn't getting fined for it's app store which is essentially the same structure as Google's OEM
They're working on that, give it some time. The complaint from Spotify gets the ball rolling. The EU will do the rest. Two or three years from now they'll have a $4 billion fine for Apple.
"Spotify announced this morning that it’s filed an antitrust complaint against Apple with the European Union, alleging that the iPhone maker is harming consumer choice and stifling innovation via the rules it enforces on the App Store."
It's not a free for all, get free money from tech companies with no legal background.
Antitrust laws aren't specific to EU by the way.