Lots of reasons.
Some folks want a gun that looks like a surviving original gun. Maybe they own the valuable antique and want to shoot a near-exact replica of it, so as to fully experience the piece, but not to risk any damage to a valuable antique?
Some folks like pre-half-wornout bluejeans too.
Matter o' fact, it's really really difficult to find genuine hard-denim clothing (needs washing 2x just to put it on) for sale these days. Some folks pay money for brand new guitars or other such items made to look old and vintage.
Some folks want everything totally virgin so they can ruin/maintain it by their own hands and that's fine too.
Patina is much more authentic when applied over
great long spans of time
.
Fakaging is an art unto itself-and like all art, some is better than the rest, and folks like different things.
I can appreciate presentation pieces that rarely see daylight staying pristine and as-crafted, but I shouldn't own them. Mostly though I personally prefer the feel of old denim and duck faded and worn until all is smooth but yet there aren't many holes or ghastly stains. I also like wood and iron well-worn by time and hands and frost and sweat and sun and snow, and such.
Everything has to be "brand new" once. Not a lot of things age as gracefully as a longrifle, and quite rare are the modern things (items of any sort) that could ever age as a longrifle. "Durable goods" are hardly that any more (they've de-engineered them down to their minimum legal definition). Lucky we live in a time when antiques can yet be had that are as yet useful as they were designed to be (tools mostly). Aye but I'm ramblin' now.
Suit yourself. Lots of guns and makers around.
This is another one of our "every Winter" topics.