Boris was afraid of repatriation as per Operation Keelhaul. This was a huge ally betrayal, an agreement reached in Crimea between Stalin, Churchill and Roosevelt. All Soviet citizens were to be repatriated under the guise that they would help rebuild the war torn Soviet Union. Meanwhile many were executed before they even boarded the transport trains. _______________________________________________________
Another thought about Samara:
Samara served as a haven for all kinds of religious desenters, like the Old Believers from Ukraine.