“-stan” is Persian/Urdu for “land of,” and it appears as a suffix after the name of the group that inhabits the territory. The names of the countries in Central Asia are all in reference to groups of people: Kazakhs, Uzbeks, Kyrgyz, Turkmen, Tajiks, etc. For a time, India was referred to as ‘Hindustan’ by outsiders. It had been adopted by the British empire to signify areas where certain groups of peoples lived.

Hence, when the original Bantustans (the ones in South Africa) were created under the apartheid government, the terminology stuck around as a collective term for the concept as a whole. Each of the actual bantustans had a name that referred to the ethnic group that lived there, and none of them included the suffix ‘-stan’. The name ‘Bantustan’ was chosen because all of the peoples who were assigned to one were supposed to be Bantu subgroups (source).