Yup - because if they don't, their Australian licensees will sue them. When HBO originally made the deals to supply content to Australian Pay TV companies, that deal almost certainly included a clause giving the Australian company territorial exclusivity, because nobody wants to pay anything to compete with the original supplier, and HBO either didn't want or wasn't able to set up its own infrastructure in Australia. So although the technological environment has changed, HBO is still bound by the terms of whatever contract it signed until it expires. There's no way to know because contracts are private* but typically entertainment industry contracts involve 10-year terms and one-time renewability options.

* though maybe you could work it out from studying companies' annual reports, and maybe some kinds of contract should involve a public filing.

(from qzervaas): Australian pay TV is a scam.

Well yeah, but you live on an island and are relatively isolated geographically, which comes with an implicit economic cost that gets amortized over everything else.