In addition to what spiceboy said, the Sydney tournament is exceptionally popular with players. The hotel has harbour views and is in a really nice part of the city, the courts are similar to Melbourne and it's far easier to get to. Hobart can be very very very very windy (there have been some hilarious tweets and Instagrams over the years), plus the tournament does not have as good facilities, is not as well run, has less off court incentives/isn't as nice a city to visit, and of course offers less money and points. Going into a slam where players aren't necessarily banking on a really deep run, Sydney is the obvious option for anyone who can make it. Sydney used to take even more of Hobart's players actually, the MD cutoff was in the 20s a couple of times before Brisbane became a Premier. The 2010 field had more star power than many PMs/P5s had in recent years.
Li Na, Estonian Mynx Nettu-GOAT Kontaveit, Aljona Ostapenko and The Barty Party
Kanepi Bertens Kostyuk Rybakina Empress Hagatha