The location was appropriate at the time, as it was convenient for power, data connections, and maintenance access, and the Comsat MARISAT F3 satellite was visible. The equipment was tested and saw limited use in 1983, as the first NSF INMARSAT call to the north happened on 1 December 1983. Official commissioning happened in February 1984. However, proposed changes to the satellite service and location would reposition the service to a location blocked by Mt. Erebus. Accordingly, the INMARSAT equipment was relocated to Black Island. It was commissioned there in February 1985.
More information about the development of what is now known as the Black Island Telecommunications Facility from 1984 to the present is presented here.
The above image is from the NSF document "Attachment 1, United States Antarctic Program, McMurdo Station, Antarctica, Communications Needs Assessment", which was an attachment to this April 2015 RFI titled "Satellite Based Broadband Communications Services."