While it is true that you can go buy something used, I've sold enough new guns to know - people will absolutely buy new over used, for no other reason than it is new.
Financially, it makes zero sense to buy anything new, except maybe underwear. Cars? Used is a better value, depreciation has hit, but you still get plenty of return on investment. Guns? Absolutely used are better values. Look at the number of high-fashion resale shops out there selling second-hand clothes. BUT still people will buy new. Convenience and being the only person to own something are intrinsic to our consumer culture. I've seen people be offered a refurbished iPhone vs. a new one - identical models and features - where the refurb is literally 1/3rd the cost of the new one and then they buy the new one. "Well, the used one has scratches on the back cover of it and I don't want scratches." - Never mind they are going to cover up the scratches with a case.
So, even if you're competing with your own previous production you can still sell new guns.
Then you add in that even though used guns are out there, they actually are often harder to come by. It may not seem like it, but you and I are the type to go peruse the stock at the local gun stores and pawn shops. Perhaps we have make an afternoon of it with a buddy, circle around town hitting the five or six places and the good hole-in-the-wall that has the odd N-Frame or custom 1911 in it. In my experience, most consumers aren't really into that. They go buy what they want/need at the nearest place and as long as it isn't outrageously expensive, they'll buy it where it is more convenient.
Finally, there is a real problem - where companies like Remington once made better guns than they do today. You know that, I know that, consumers know that, gunshops know that. More than once I've seen a 40-year old .30-06 ADL sit next to a brand new .30-06 SPS and the SPS is half the price. Consumers buy the cheaper gun.