Because it was deemed too violent and rejected by the censors. Furthermore, part 7 "The Feast of Steven" was a Christmas episode in the middle of a Dalek adventure, so that episode wasn't sold to any country.
In the 1960's, film prints of Doctor Who were generally only sold to countries in the British Commonwealth(the US didn't start getting Who until Pertwee in the 70's). The first offer for sales went to Australia. If Australia bought them, then they would in turn be offered to other countries, such as New Zealand, Singapore, Ghana etc. If however, Australia refused to buy the serial, they were not even offered to other countries. It's somewhat more complicated, and has to do with rights, royalties etc. When the Australian television people watched The Daleks Master Plan, they deemed it too violent, and refused to buy it. Thus, no other countries were even offered the serial.