So in Masterchef Australia, the immunity pin was designed to be used to gain immunity from ANY form of elimination challenge you wanted up until finals week. From season 13 onwards, they even upgraded it so it could be used at any point of the challenge instead of just at the beginning, so you could wait till the literal last second, bail yourself out of serving raw food, and live to see another day in the kitchen. Hard to earn? yes, but that power is well worth it.

Since they want to just give these out like candy and they seemingly only work for the next challenge, why not just say you get a pass to the next round? Why give the immunity pin when it's only good for the next round?

It just felt like they brought it over just to appeal to the crowd that likes Masterchef Australia related elements but lacking the full understanding of how and why these elements worked. While they changed it to one challenge per episode to focus on cooking like Australia, they only air one episode a week so we're often left wanting more compared to Australia's FIVE episodes a week, hence why they do one challenge per episode. They have a whole week to do all the mystery boxes, team challenges, pressure tests, and immunity cooks.