here is one of paul's early works http://www.google.com/imgres?imgurl=http…
the first thing you will notice was how bad he was. this is important. it's important because it led him away from doing anything conventional. so to get to your question, he painted that way because it was the only way for him to paint. if he were a great painter of people he would have been doing tradtional portraits.
if you flip your example you will see it looks just as bad upside down as it does rightside up. that means abstractly speaking he had no compositional filter. he just painted stuff without thought. so to get to your question, he didn't paint to be pleasing to the eye nor was he painting anything natural,,,he couldn't. cezanne was the first to "intellectualize" art. from which sprung intellectualizing cubism et al going forward.