Maybe they already will did have done. But not yet.
If you think of it, it is very logical: The events leading from one point in the past to a point in the future must actually have time to happen. Imagine you obtain a sophisticated piece of technology from the future (lets say a ship) and you extract the technology (you will probably need some months for that). Then you analyse it (will at least take several months), copy the technology, sell it and thereby giving birth to a new age of computer-technology. Eventually smart-phones, Stackoverflow and Curiosity will be developed - all based on that technology. All of that takes time.
At one point this technology will be installed on a ship with a warp 5 engine, and centuries later even on a ship that can travel through time. For all of this to happen, it takes time.
Now if you look at the events in Abramsverse from the 29th century, it takes no time at all, since from that perspective all of it already happened. But from Spock's perspective it will take centuries until all those things will have come to pass that will be noticed by the Relativity as a change, as a deviation from the way things are supposed to be.
The Relativity will probably intervene, but not before it happened. Since from their perspective it already happened, they will intervene instantaneously, but that's not the perspective of Spock. He has to wait until the chain of events unfolds that will lead to the intervention of the relativity.
 This is not Timey Wimey Stuff this is Future Semiconditionally Modified Subinverted Plagal Past Subjunctive Intentional.