You can blame Stalin for wanting to establish borders along ethnic lines there. Ironically though, one of the Uzbek enclaves has a 99% Tajik ethnic population.
I just found your account and, safe to say, I feel blessed. I utterly adore these 'old map' quizes and was beginning to run out of the ones the site was feeding me. This is another chip of the good block and an interesting view, perhaps, into how different our modern boders are from what was relevant to the tibetans then.