Many players DON'T want future technologies. Civ3 would then lose the 'realism' effect (no, not everything in Civ3 is perfectly realistic, but it is realistic enough), and the object of the game being to re-shape 'history' (not the future).
The CTP series went over-board (over did it) with the future stuff.
I'll pass on the War Walkers and the Eco-rangers. One thing I like about Civ3, is that the buildings and units are familiar to me, so I already have a very good idea of what they do instead of needing to look in an instruction manual all the time. Everyone, whether a serious gamer or not, knows what a tank or a battleship is, but how many people know what a storm marine, swarm, or phantom is or does in the game? (I believe they are all outer-space military units for those who were curious).
CTP offered more governments, that is true. CTP, however, almost always forced you to change governments, because there was a better government available (you were limited to the # of cities for each government or else you gained an unhappy citizen in every city for each city you go over the 'limit', one government allowed 10 cities, another 20 cities, another 30 cities, etc.).
With the current method of changing governments (for non-religious civs), I can't imagine having 4-8 turns of anarchy 10-12 different times!
The 'invisible' units were nothing but a pain in the rear. Don't want to see them ever again.....Oh wait I couldn't see them because they were 'invisible'

. Seriously, they were nothing but annoying and a minor nuisance.
Other than the invisible units and the 'space'/future units, there wasn't any other units or major differences, was there?
detail to economic strategy
Perhaps an 'economic victory' condition? I would support that idea.
Yes, the tech tree in the CTP series was more diverse, allowing you more choices in which direction to research. Of course, eventually you would have to research everything, but it allowed you to go further along one branch of the tree for a longer period of time (now only if the tech pace/turns to research wasn't so freakin' fast as it was in CTP).