Because those things are controlled experiments. Because we don't understand ALL of the processes that are at work in the real world, one attempts to limit the outside influences to test the things that are most easily testable. As we begin to understand what affects a certain process, then we can relax those restrictions and understand what happens with other processes.
Science doesn't get into predicting the future because it would need an extremely complex model that would accurately examine every aspect of life on the planet. Think of the computer hardware that would be necessary for such a thing. Since we can't do that, we do controlled experiments on the things that are easy to understand, and perhaps, someday, we'll have that model.
That's why predicting the future is not a feature of science. It can't. Yet.
So the mantra, "In order for it to be a theory it has to be predictable" can be tossed out from time to time. Predictability suits evoltuion theories very well when it can be applied to the past, but where observing the process of evolution is concerned, nosiree. Can't have predicability there.
You gave Chuggy and opening here, because he is taking it that the TOE is not predictive of scientific discoveries in the future. The TOE has been predictive of fossils we will find and genetics etc. It will be again.
So, to a certain extent and in a creationists simple mind the TOE DOES predict the future.