Because, whatever the changes made for enhancing one area of operations or another, the Odyssey is still a Cruiser, made first and foremost to have the strongest defenses in the Fleet. It's true that the Tactical Odyssey is built more for combat than the other two versions, but not at the expense of its primary purpose in the Fleet.
From a game standpoint, Cruisers are all Engineering-centric. For more emphasis on Tactical than Engineering, you would go to the T5 +1 Escorts, such as the Armitage or MVAE, while for similar emphasis on Science, you would go with the Atrox or Long Range Retrofit (though the Advanced Research Retrofit would be closer to an Odyssey, it doesn't have equal Science capacity to the Long Range Retrofit).
In short, if the Odyssey had more Tactical or Science slots/BOFF stations than Engineering, it wouldn't be a Cruiser.