I don't know much about the TV series but if it is in any way like the OVA then it is liable to have a more mature rating than many other anime, which are largely aimed at boys and girls. Maybe they are looking for something they can market to a more adult audience in light of the relative slump (or levelling out) of the overall Hollywood movie scene. The fact that Production IG was involved is also a lure, which will make marketing of the final product that much easier for them. There are a number of reasons they could have chosen this as a candidate and without asking whoever is responsible for these acquisitions we will probably never know.
(I was relatively unimpressed with the Blood OVA and so was uninterested in watching the TV series.)
Naruto was a special case, which largely got licenced due to the official merger between Viz, ShoPro and Shueisha, each of which had a hand in the overall project. Short of that the actual cost of licencing the show would likely have been astronomical. Blood+ on the other hand at only 52 episodes (rather than 3 times that) and not nearly as popular, is liable to be far cheaper. If they licenced something of the size and popularity of Naruto they would be potentially heading up a lot of costs with very little return if they should fail. Something like Blood+ is a much safer choice because you have market familiarity (with Production IG and the original OVA) and a known and fixed length.