I was thinking about this myself. Ultimately, it's because the Avengers brand has recently become a juggernaut on a level the X-Men used to be on, and tying this book to it is the only way to guarantee sales.
I do think the title is a bit awkward, to say the least. It looks even worse on the covers, with the two titles the wrong way around (although having said that, "The Initiative Avengers" looks a lot less awkward, and makes about as much sense).
With the other two Avengers books having the same banner across the top, the cover looks almost like Avengers #1. Which I guess is exactly what they want you to think.

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