Welcome! Thanks for coming and sharing your question here. I hope we Forum folks can be of service to you as you explore this and other questions you may have.
I’m not a biologist, but I like to play one on TV. (I’m a linguist, but I enjoy talking about biology avocationally here.) This is one I question I may actually be able to field, but I’ll let other people correct me if I’m wrong.
Mutations just happen. They happen randomly with respect to fitness. That is to say, some mutations are beneficial, some are detrimental, and a large number are also neutral, neither good nor bad for fitness.
After mutations happen, natural selection occurs and it is this that decides whether an organism survives and reproduces and dominates.
So let’s imagine some other place… let’s say a deciduous forest in Pennsylvania. Lots of herbivorous white-tailed deer there. Let’s imagine that the mint mutates in PA to lose its mintiness. Will it survive and reproduce? Well, perhaps for a time, because deer might be smart enough to recognize it and steer clear. But the point is that eventually, one of the many herbivores in that ecosystem will take a bite, and they’ll realize it’s not so nastily minty anymore, and then that variant will wind up disappearing before it takes over. The mutation will result in negative fitness, and it will naturally get weeded out.
Contrast this with Hawaii. There, the same mutation happens, again randomly. This time it has no effect on fitness. It doesn’t “know” anything. But the environment fails to shape the destiny of this variant to destroy it. So it survives and reproduces. Perhaps it naturally takes over (could be a dominant gene), or perhaps it has an advantage over mintier mint because it doesn’t have to commit resources to creating its mintiness.
Does this make sense?
The same could be said of island-bound flightless birds (e.g., kiwi), humans’ inability to create Vitamin C, and all kinds of other such mutations.
Hope this helps. Feel free to ask follow-ups, of course.
[Edit multiple times for typos.]