The reason for carrying gear is three fold.

First is time.
Sure I can start a fire by rubbing 2 Boy Scouts together. Standard primitive skills training. Scenario I just fell through the ice. I'm soaking wet and my cloths are freezing stiff. The seconds or minutes between using a match or lighter versus constructing a bow drill and getting the fire going. That little bit of time could mean the difference. So gear buys you the time it takes to make the tool to make the tool you need.

Second is quality.
Sure I can make a cutting implement from the things I could find around me. But a steel knife blade works a lot better and lasts longer.

Third is confidence.
If TSHTF tell me you will not feel more self assured just knowing that the gear is available. That alone may make the problem smaller. At least in your mind and therefore easier to over come. Remember panic can kill you quicker than just about anything else. Just the time of breaking open a kit puts your mind in survival mode thinking. It keys your thinking from the situation back to your training.

By this do I mean forget learning primitive skills HE Double hockey sticks NO!!!

The skills are a great back up if your gear is lost, damaged or inadequate. Also if things last longer than expected they can improve your lot in the situation. Is gear the end all be all. No. You can only carry so much. How you use it, the skills to use it and the ability to make what you need from what is available is how you survive.

Ok in your local area you are close to civilization. But you broke one or maybe both legs. Regardless of your skills you ain't going anywhere or any other injuries that anchor you in place.

Why a whistle. Your stuck in a hole where you fell causing the injuries you have. You here search parties looking for you. You did leave your plans with someone so they are looking for you. You cry out. What issues from your mouth is a croak barely above a whisper. You yelled out your voice hours ago. The whisle summons friendly folk to get you to aid. Need I say more. But you say I can whisle so why carry one. Try it some time with a split lip. Facial injuries are possable too.

Mirror. As above. Not only can it signal for help but it works as a mirror. Helps you treat that split lip or any other injuries that you can't view directly.

For any other gear there are similar reasons.

I live in central Pa. While heavily populated there are stretches where there is nothing for 20 and 30 miles. Then think of places like Canada and Alaska you can be talking in hundreds.

Then because of terrain, injuries or both you can't travel. And you may not be able to hunt or trap effectively or even fashion the gear to do so. So plentiful game might not be readily available. Or it could be the season. Need more be said.

Most kits are designed to be area specific but they also cover enough generalized gear to work after a fashion anywhere.

I have spent many days wandering in the wild breaking out nothing more than my knife. But you better believe I carry emergency gear just in case. As for a 50 pound pack but if I tried to carry that much with my back. It would probably kill me quicker than the wild woods.