Because free will is an illusion as science has conclusively proven. (not.)

What would really settle the issue would be the ability for neuroscientists to predict the actual outcome of more complex decisions prior to the subject being aware of it themselves. That would, in a very true sense, prove that free will is indeed an illusion.  We have no free will as far as the initiation of our movements are concerned, but that we had a kind of cognitive “veto” to prevent the movement at the last moment; we can’t start it, but we can stop it.  The brain starts to unconsciously churn in preparation of a decision, and once a set of conditions are met, awareness kicks in, and the movement is made.  Stefan Bode, his detailed fMRI experiments showed that it was possible to actually decode the outcome of free decisions for several seconds prior to it reaching conscious awareness.

http://io9.gizmodo.com/5975778/scientific-evidence-that-you-probably-dont-have-free-will