I have several theories, but I think it's prolly that most people can't appreciate the utility of a knife until they've been carrying one... And today it's easy to get something else (like from the next room to open a box) than to just take 5 seconds and take a knife out, use it, pocket it. They never get that 'Wow, that was quick, easy, and useful' feeling that we know and love.
I see a lot of people on here that have had great success in getting people just a cheap knife and going 'take it, you'll thank me later' All my friends now carry some sort of knife, and at least 2 have converted some of their friends. (Kershaw Scamp is coming for Christmas for some.)
The only hard part is getting those people who look at you funny to realize 'useful' is not weapon. This thinking doesn't work for anything else really. Think about it: the guy walking to home plate with a bat is not going to commit a hate crime against the man wearing the catcher's mask, and I'm not going to stab the cashier with the tool I've been opening boxes with all day. I find words work well. Then again, I sharpen my silver tongue as much as my knives, so...