Knives are generally a lot more useful than most other tools. I use a knife a hell of a lot more than I use a hammer or a saw or a wrench.
Knives also have a lot of variation. A screwdriver is a screwdriver. You get flat and phillips and that's it. They also don't need to be of high quality and their appearance is not very inspiring.
Knives on the other hand have inumerable variations in blade shape, material, grind, finish etc, and quality is very important. You also have sheathes and folding knives to consider (thus lock mechanisms, leatherworking etc all come into it).
Knives are far more versatile than screwdrivers or hammers. 99% of a hammer's work is hitting nails. 99% of a screwdriver's work is screwing things. Knives can cut rope, cord, string, fabric, food, wood, packaging, boxes, dead animals, opponents in combat etc etc etc. They can carve, slice, skin, chop, saw...they can do a huge variety of things.
THey're also very attractive - sleek and elegant or brutish and masculin. Some knives also have connotations with combat and fighting which are interesting in themselves.
Knives are relied on more than almost any other tool. If a screwdriver breaks, you go get another one - big deal. If a knife breaks, you could burn to death, freeze to death, starve to death, be killed by an attacker, even die of thirst.
Knives take a lot more skill to make than most other tools, I think. Anybody could bash out a flat headed screwdriver or a workable hammer, but it's very hard to make a good knife.
Also most guys like things that are loud, sharp, and shiny.
But, to be honest, I've been into swords, knives and archery for longer than I've been interested in guns. Perhaps these are "gateway hobbies" that lead into harder stuff like guns. 
