What exclusive regional rights gives is an effective monopoly. Generally speaking we don't allow monopolies because they are bad for our economy - they inhibit innovation, the supply inferior products or services at inflated prices. This is good for the (right holding) business, but bad for consumers. Not quite sure why/how content escapes anti-competition laws.
People mis-use and misunderstand (far more often than not, it's not deliberate - just through a lack of understanding) what the Commerce Act is concerned with. For example, s 36 proscribes against undue taking advantage of market power to (a) restricting the entry of a person into that or any other market; or (b) preventing or deterring a person from engaging in competitive conduct in that or any other market or (c) eliminating a person from that or any other market. People too often think, for example, "Apple only allows iOS on Iphones and Ipads and, therefore, Apple has a monopoly* in the iOS market". But that ignores the reality of the substitutability of operating systems. To an extent this would also apply to content rights. It doesn't make sense (at least not from the sense that the legislature drives as, as determined by our courts) to say that there's a "market" of only HBO shows and Sky has them all and, therefore, they have market power in HBO shows and if they refuse to share these with Spark and whoever else, they are abusing their market power. This is because there are potential substitutes and sometimes end users do benefit from one market player having all the content of one group of people etc.
I am not saying the law always get things right but a lot of people's concept of a market, what is market power, and what constitutes a monopoly simply do not take into account many concepts central to our competition laws, e.g. substitutability.
* Note that this word should not be confused with the concept of market power. They are not one and the same.