The more I think about it, the more I realize that it's because, by accident or design, the storytelling is subtle. Yes, a movie about robots whaling on each other has subtle storytelling. There's loads of minor plot points tossed out during the course of the movie, but a great number of them are resolved by showing, not telling. There isn't a "rub it in your face" moment for every resolution, often it's left to a single glance to reveal how it played out, or the viewer is required to do a little extrapolation themselves. Sure, maybe they wrote and even filmed a lot of "and here's how this played out" scenes but cut them for time, but regardless of how it happened we were left with just enough information to figure out how everything worked out.
Of course, it does mean you have to be paying attention, and have your brain engaged during a Big Action Movie. I figure a lot of viewers won't be doing either, and will be left feeling that the movie was full of danglers. And that's fine. The people who aren't paying much attention probably don't care about the danglers anyway...they're there to watch robots smash each other to pieces. They don't care if Hugh Jackman's character has come to a realization that his philosophical stance of "the fight's not over until someone's on the mat" is invalid, or if the future of robot boxing will lie with AI like Zeus or human-controlled bots.
Oh, I'm not saying it's great storytelling. The acting is often a blunt instrument. But it's refreshingly subtle for a Big Dumb Movie.