It's a very strange move indeed. maps.google.com implies an application lives there, far better than being on the root domain. It also means that when you start typing maps.google, you'd get all your history searchable related to maps, although arguably that's useless. I can't think of a reason why this would be a good technical move for Google (ignoring the don't do evil thingie), other than simplifying... certifica…
Other things: slightly simpler external DNS surface, probably tiny speed improvements because users only need to have the IP of www.google.com, not one for maps, one for www, one for whateverelse. More possibility for connection re-use, as you'd only need to have a connection open for www.google.com, not one for each service. And security wise: ISPs can now only see that you're accessing something at google, but not…
I don’t buy the simplicity argument for a second. The infrastructure exists, has existed for many years, and is not particularly exotic in the world.
The only thing that matters to a surveillance and advertising company is surveillance and advertising. You don’t need to overthink this one.