There are no dingos on Tasmania is the short answer to why the Aboriginal population there did not associate with the dingo in the same way as Australian populations.

As to why no dingos are present on Tasmania-- for that your best bet is to ask a paleo-biologist. It is very likely that the dingo derives from the dogs brought by Austronesian or Papuan speaking peoples between 7000-3500 years ago. These dogs (or dog like canines) would have come down through Island South East Asia and into Australia where they multiplied and spread and adapted to the harsh environment. As there were no voyagers down in the South of Australia or strong maritime contact between South Australia and Tasmania, there was no one to carry the dingo across the sea.

Dingos arrived in Australia sometime between 3,500 BP and 12000 BP, a sizeable time after the first humans arrived in Australia and in Tasmania. Tasmania was separated from the Australian mainland by rising sea levels around 12000 BP.

In other words, dingos arrived in Australia after Tasmania was separated from the mainland, and were never carried over to the island.