Speaking for myself, I don't view knives as some "gateway" hobby into the gun world, as knives are their own seperate universe. I like knives way better than firearms as a hobby.
I add to the voices that view knives with more satisfaction than guns because knives can and are used daily and in my best years financially, guns are used way less, when I have the time to go to the range, when the weather is cooperating, or during defined hunting seasons.
Additionally, only a comparative handful of industrialized nations produce firearms whereas knives are a truly global pursuit. Off of the top of my head I have knives from the US, Canada, Brazil, Costa Rica, Honduras, Sweden, Finland, Germany, France, Italy, Switzerland, Russia, Japan, Taiwan, and New Zealand. That representation can mostly be done with firearms, but it'd probably only be doable via a C&R. And the knives don't need funky ammo either.
Knives have a better reselling market than do firearms in that you have a far broader pool of legal buyers, again going all the way overseas if one is into high risk internet selling. This makes a knife collection far easier to acquire and/or turn over if one wants to raise cash for different pieces.
I get far more satisfaction using a puukko and axe in the woods to make a fire in a downpour than I do pulling the trigger on a buck--the only thing that has made the latter from getting old is the thought that I'll get to try a different knife to dress the game.
One last thought, knives can easily be as expensive as most firearms commonly bought and sold since the custom market in knives has a lower entry point that still isn't cheap. I am spending about $375 on my next folder after optioning it up a little.