It has because of necessity and evolutionary time. It's quite natural for everyone to wonder about it. But it has an answer. It's not quite that simple. Some things would take an infinite amount of time.
Evolution is feasible in linear time.
This is what happens as the length of the sentences you are waiting for the monkey to type by chance grows. Trying many combinations by paper and pencil or by computer requires trying each possibility, one after the other. It is interesting to watch how such evolution-simulations generate structure out of simple elements without any human guidance.