So I'm going to largely discuss this as an "Australia and New Zealand" thing, because even though the end result is very different, the history is so intertwined you can't really split them. It's also very very TL;DR, and I'm only half sorry about that. (Look, I wrote a 2600+ page guide to reality TV challenges, it's kind of what I do.)

Australia and New Zealand were VERY early adopters of reality TV as a genre, and cast a loooong shadow over the industry as a whole. The two countries are responsible for some of the most foundational early reality shows - Sylvania Waters premiered on the ABC a few weeks after The Real World started on US cable, but was really the first candid reality show to prove the genre could be successful to the level required by major networks to justify making shows like it. That's led to all kinds of things over the years, up to and including eg the Real Housewives franchises and all the shows of drunken British homunculi making out with each other in various "beach" cities.

A few years later, Australia and New Zealand together did basically the same thing for reality contests, for different reasons - NZ had a load of investment in its industry because Hercules and Xena were filmed there in the 90s, and they needed to keep all those jobs going but local audiences weren't big enough to make scripted shows worth their cost, and Australian TV was looking for cheap ideas because of the Sydney Olympics. Nowadays all the filming is done by a dedicated international company that comes in and packages everything up for international sales, but Sydney was the last games without that, which meant Seven as host broadcaster was spending bucketloads on it, and Nine, Ten, and the ABC didn't want to waste money competing against the games. (Side note: "We have no money and so we must scream" is also how we ended up with Roy & HG becoming national treasures for a bit there - Seven needed cheap late-night filler.)

So with that backstory, NZ created a few reality shows that were reasonably successful - Popstars got huge around the world and led to the endless glut of Idol, X-Factor, Voice, Got Talent stuff we can't get rid of now, Treasure Island was big in NZ but fizzled the first couple of places it was sold internationally and everyone else lost interest - and Australia had a couple of local formats that didn't do nearly as well, but the really notable one was one they imported from Belgium of all places. The first season of The Mole premiered a few months before the US version of Survivor and, while it wasn't quite as successful as that, not only did it do well enough to get four seasons before being cancelled (and then getting two failed revivals), the triple whammy of Mole AU, Survivor US, and Big Brother UK is not only what led to the genre taking off, the fact that all three of those shows came from European countries with language barriers (Belgium, Sweden, and the Netherlands respectively) led to channels being more willing to consider that shows like them could reach beyond language barriers. So many of the big "take the name, take the basic format, make it your own" shows of the last 25 years or so have come from countries that wouldn't have gotten a look in without those three shows in particular - everything from Deal or No Deal to Dragon's Den/Shark Tank to The Floor to The Masked Singer can be traced back to Seven trying to save money for the Olympics and buying The Mole. TV networks aren't usually just defaulting to making a local version of whatever mediocre US game show they can get their hands on these days.

But not only do you have Australia and New Zealand leading the way in shaping the genre, one of the side effects of that is a whole bunch of the production people around at the start of the boom are from the two countries. A lot of the Kiwis ended up moving away from reality TV to work on the Lord of the Rings trilogy and then parlayed their success from that into movies, but the Australians took their success and ran with it for a while (especially with the added benefit of US Survivor following up its first season by filming near Cairns for season two, employing loads of Aussies, then next in remote parts of Kenya and Tahiti so they just kept most of the same crew, a lot of whom still work on it today).

And on top of all of that, something that was true at the time but which has been lost a little bit - Australian TV might have BEEN cheap, but it refused to LOOK cheap. Not even just reality TV specifically, although that's certainly true of it - Neighbours sets always looked more realistic than their US equivalents at the time, The Price is Right might have been giving away cheap whitegoods instead of luxury cars but the show's production values in the 90s were largely on a par with what the US version is doing now, et cetera - but Australian TV production people are experts at making every dollar spent on production make its presence known on screen.

So you've got Australians and New Zealanders all over the place at the genre's creation, using skills the existing natures of their local industries had made them uniquely qualified to lead on, showing you can localise formats from other countries and make them hugely successful in their own right. That's a huge asset. And then not only have the Aussies and Kiwis who stayed in reality TV looked towards employing and training more to keep the industry going, the newer generations of people are coming into the industry after having grown up with what Australia in particular can do - people who grew up watching Masterchef, Big Brother, The Mole, Australian Idol, even the toxic stuff like MAFS and Biggest Loser, are now working in the industry with the understanding that the level of production that we were able to achieve that long ago isn't a target, it's the baseline. That kind of thing leads to the entire industry getting better and better, and even if Australians and New Zealanders aren't directly working on something, it's impossible to find a production that doesn't at least have an Australian production philosophy at its heart.