Well, lets be clear. Most of the 'convicts' were petty criminals, there were cases of kids under 16 being deported for stealing an apple, or a silver spoon.
The POINT was that we needed people to go and populate the new land we owned, and tough, working class 'criminals' streetwise and able to survive were the ideal material. So anyone of that ilk was basically singled out to help populate the new country, under the guise of 'punishment'.
Many countries with colonies did this, France in particular. France transported convicts to Devil's Island and New Caledonia in the 19th and early-to-mid 20th centuries. Devil's Island, a French penal colony in Guiana, was used for transportation from 1852 to 1953. New Caledonia became a French penal colony from the 1860s until the end of the transportations in 1897; about 22,000 criminals and political prisoners (most notably Communards) were sent to New Caledonia.
The most famous transported prisoner is probably French army officer Alfred Dreyfus, wrongly convicted of treason in a trial in 1894, held in an atmosphere of antisemitism. He was sent to Devil's Island. The case became a cause célèbre known as the Dreyfus Affair, and Dreyfus was fully exonerated in 1906.