Colonial/settler governments tended to go hot and cold on immigration based on the political and economic cycle and it is important to remember that when looking at places like SA or Rhodesia.
From the Decolonisation era mass European migration makes a lot of sense to South Africa/Rhodesia, whereas the same was very attractive to NZ and Australia after WW2, when both countries drew the conclusion that they needed more Europeans /population generally.
If SA/Rhodesia were so inclined the 1920s would have been the perfect time to encourage migration from Europe, but at the time, the stomach was not there for it
From the Decolonisation era mass European migration makes a lot of sense to South Africa/Rhodesia, whereas the same was very attractive to NZ and Australia after WW2, when both countries drew the conclusion that they needed more Europeans /population generally.
If SA/Rhodesia were so inclined the 1920s would have been the perfect time to encourage migration from Europe, but at the time, the stomach was not there for it