I was under the understanding that Apple never originally really intended people to use the Unix side of OSX and that the whole command line standard Unix utilities became commonly used in spite of Apple's design. I could be wrong.
I have no idea if there was a conscious choice either way. However the goal was certainly, "Our cooperative multi-tasking system where any bad application takes out the operating system no longer cuts it, migrate to a preemptive one." And building on Unix was the shortest path there.
