Numbers be damned - that chart says it all. In comparison with other Xbox Live titles, Halo 4 was just not well-received. Sure, it's impossible to say from that chart that Halo 4 is a good game or a bad game, since it's all relative as far as the chart is concerned, but you can say that compared to the other titles available during its lifespan, Halo 4 just isn't as well-liked by players as previous Halo games were.
Of course, we all know that in reality, we can go beyond what we can say from that chart. Halo 4 is pretty damn bad, and that chart just confirms it. If anyone at Microsoft has a brain (and I'm sure they do), they're looking at these numbers and they're scared. Sure, they got their sales of Halo 4, and they're happy. But they're also looking ahead at future sales of any future DLC, and more importantly, sales of Halo 5. If you don't keep your dedicated fan base interested in Halo 4, they're not going to purchase Halo 5. You may have your money today, but you're still going to need money tomorrow.