In 1865 Italy was a bit preoccupied with domestic matters. The Italian Unification process didn't end until 1871. Govts were changing every 6-12 months in that decade. Against that background it is hardly surprising that the acquisition of the Nicobars wasn't pursued. Britain acquired them in 1868/69.
Takes me back to school and my European history days.
Only after it had sorted its internal problems could Italy begin to think about building an empire, and so it was 1882 before it took over an Italian commercial coaling station at Assab Bay established in 1869 to cash in on the opening of the Suez Canal. So Italy came late to the imperial table.