I think there were some historical artifacts there. With the Senate, I'm not sure about the way the process works in Canada, but theoretically the Senate in Australia is known as the states' house, as you may be aware, and was originally established to be a house of review for the states, so a different electoral system was developed.
Each state has a constitutionally guaranteed minimum number of senators. A quota system was developed to help fill that number. The only difference is that each of the six states has 12 senators who complete a full term of six years, and the two territories—the Australian Capital Territory, where Canberra is, and the Northern Territory—have two senators who complete a three-year term. It's just a different process that emerged, and people seem broadly comfortable with it, as noted in the comments I made previously about the recent changes to the Senate electoral system.