Habit mostly.
12 years ago. I worked as a tunneling engineer. Underground it was mandatory. Self rescue was very real. We had to control the flow of air with the use of heavy canvas bulkheads. In a fire, you wold have to cu yourself out.
Now? I flip between a Swiss Army knife and a regular knife. I use one every day from cutting a hangnail to slicing my lunch avocado. I wash it nightly with my dinner dishes.
It’s just so handy when you need one. Same reason I carry a flashlight all the time. Blackouts are very real around here. Plus peeking into dark crevasses
Pocket knives are a billion dollar business.