MacOS's package manager is the App Store. Which Handbrake isn't on.

It isn't on the Windows store either as far as I can tell.

Why, I don't know - maybe nobody involved wants to pay the fees to become an Authorized Developer, maybe there's a Free Software religious argument going on, maybe Apple doesn't want a program whose original function was "ripping DVDs" to be on there because of the many deals they have with the entertainment industry.

tl;dr: the program in question ain't in the operating system's package manager.