1. Unfortunately with all the red tape and government controls selling a gun is a lot of trouble these days. So you have to be willing to spend the time and deal with the hassles of selling, which many people just do not do. If you were a business it would be right to sell, but from what you have written I don't think you are a business.
2. Even if you do not have a personal attachment to the gun, it may serve some purpose such as a truck gun, a gun you leave near your sleeping quarters, or a gun you don't mind carrying in your tackle box.
3. Also even if you could get a little more for what the gun is worth right now, it is difficult to replace it with something less expensive and of the same quality. This is because buying on line you pay shipping and FFL transfer. Buying locally you pay sales tax. These fees and taxes have to be added in to the purchase price of a replacement gun.
4. Good quality guns serve as one form of hedge against inflation, with more utility than hard currencies like gold or silver. The gun may well be worth more in 5 or 10 years than the cash you get from the sale would be in 5 or 10 years.
5. In a worst case scenario of SHTF, guns will be on of the most valuable commodities to trade, next to ammo.
6. Law of gun inertia states, "Guns at rest in a gun safe tend to remain at rest in a gun safe."