Why? I say if you can afford it (or often "barely" afford it) why not?

as the saying goes, You get what you pay for, and it's true.
You want a crappy meal? Go get some fast food, but pick up some pepto an the way home. You want crappy wine? Go buy yourself a box and stick it in the fridge, and prepare for the headache. You will find me at a decent restaurant enjoying a $10-20 glass of wine and chowing down on a decent steak, and to me it's worth every penny.
When I own a really nice knife, I take pride and truly appreciate the unique design, materials, craftsmanship, beauty, and often rarity of the piece of "art," knowing how much time and attention to detail went in to creating operational excellence.
Sure, I could buy a $10 knife an it will open letters just fine, but over time, you get what you pay for. $10 knives feel cheap, and they are cheap. They will not hold an edge, break easily, and over time, be useless and worth nothing. Yea, you might say you could go buy another one... But why? Why invest in a tool that is crap and will fail? Once you own and hold a quality knife, you will NEVER go back to a crappy one.
There are many decent knives under $100, but I prefer really nice knives, and many are well over $200. Overpriced? Sometimes they are, but these are not just expensive knives to me.. They are collector pieces, art, and investments that will pay off in pride of ownership, efficiency, dependability, bragging rights and resale value.
And the fact that my wife could care less is priceless.
I hope that shed some light on knife collecting, and why we like quality knives that happen to cost a fortune at times.