Argh that question is back!
Its been gone over a few times but CeZeus has hit the answer in a nut shell. Stardock want Galciv to be about ruling a civilisation as 'emperor', it's not about being the admiral. That's the design decision and the ultrimate answer.
There are some other supporting reasons, perhaps the main one being about AI. Moo2 is the big comparison ofc. In Moo2 you could design your own ships and fight tactical battles with them. Or if you chose to you could just hit auto and the computer fights for you. Good in theory, but in practice the computer never used your ships as well as you knew you would have done, so the nagging temptation was always there to fight every battle to get the result you know your fleet should have gotten.
But now you're fighting every battle no matter how minor. Not great. The fundamental problem is that the AI is never quite as good as the player, so you're always going to be fighting the battles yourself (I realise that someone won't agree, but this is true for most players). Once you get to that point the focus has shifted from strategy to tactics.
Also, bear in mind the the Moo series was primarily war focused. Yeah you could take other routes but the game was biased to military solutions. GalCiv is about choosing you civ's path, be it diplomatic, warfare, technology or whatever, so it's less important to focus the game in on the combat. Putting in a tactical mode shits the games focus to a military end game as you are commiting alot of resources to making tactical combat.
So for the purity of the design, Galciv has no tactical combat.
