Def: "the exclusive possession or control of the supply or trade in a commodity or service."
Google has a very nice search engine but I personally fail to see how they control the supply enough to be considered a monopoly. Sure most people use them, but that is by choice. There are viable alternatives.
The 160 page document[1] is very comprehensive, and worth a read. There's a few surprising things in there. The way they manually adjusted the algorithm several times specifically to demote "comparison shopping engines" (CSE) is very telling. Their manual testers liked CSE properties, and found the results relevant and useful. Google kept changing the criteria and questions until they found a combination that justified demoting them...so that their own CSE would get more traffic.
One of the conclusions: "Google has unlawfully maintained its monopoly over general search and search advertising"
I can't find anything that says that's the reason action wasn't taken either.
This says a lot more about why the FTC didn't go forward with its staff's recommendations to go forward with charges than anything else.