This Bach chorale composed by machine learning is pretty good

Gaetan Hadjeres and Francois Pachet at the Sony Computer Science Laboratories in Paris created DeepBach, then entered Bach's 352 chorales. The resulting composition is certainly in the style. So why does this work better than some other attempts? Part of it is the sample size of compositions. Another part is the chorale's formal structure (four voices, simple patterns of notes and harmonies).