Early morning thought:

Near as I can tell, Joseph did not go around the region warning people of the coming famine.

Was he put under a gag order by Pharaoh?

Did he lack confidence in the accuracy of his interpretation of Pharaoh's dream?

Was he worried that warning others could endanger his comfortable position as second in command of Egypt?

As second in command, I have to believe Joseph had resources at his disposal which could have been used to send a warning to his father. 'Start storing feed and food now.'

Was there resentment in his heart toward his brothers that prevented him from sending this warning?

I'm not being judgmental. The guy remained faithful to God even after being delivered into slavery by his family, and then doing time for a false rape charge.