It's not a distraction think of the question as a general: why should service X be allowed something that service Y is not? There are still really good reasons why X != Y (or conditions that would cause seemingly equivalent X and Y to be evaluated differently). Perhaps the FCC needs more education on the subject. But more likely there is absolutely no rational rationale behind this action.

Google is a de facto monopoly.

No, it's really not. There are alternate search engines like duck duck go and bing, alternate email providers, photo sharing services, etc etc.

There were alternate operating systems in the 1990s, but Microsoft was still found to be exercising monopoly power.