Lots of good points made above which I agree with and which personally apply to me.
And a couple of others which apply to me:
1) My Financial Advisor accurately calls me an 'accumulator' when it comes to my hobbies. And these accumulator tendencies are exaggerated as availability of items goes down, and costs continue to go up. It happened last year with electric assist bicycles. Both my wife and I ride them, they are great for our health (well, mostly great as my wife is still recovering from a fall and broken elbow & scapula, so our daily riding is on hold for now). During the peak COVID lockdowns the e-bikes allowed us to get outside, get healthy exercise, and maintain some level of sanity. But with a huge demand spike and interruptions in the supply chain, e-bikes were quickly sold out and became unobtanium. So I bought a small 'fleet' (different bikes for different purposes, extras to have when friends & family visited and wanted to ride with us, etc.) They weren't getting any more available or less expensive, so I bought what I wanted when I could get it, especially if it was discounted at all being 'last year's color' or something like that.
The same has occurred with air guns for me. Backyard sanity tools for when you can't leave the house and go do stuff. Buy them when they are available as they aren't seeming to get re-stocked very quickly and we've already all complained about the price hikes with the value of the USD going down so badly against other less-mismanaged currencies.
2) Many of us don't have a shop of big local club we can go to and try out different guns. So we have to take for granted what YouTube (paid or not) reviews say, as well as the opinions of our fellow shooters. These reviews and opinions can all be spot-on and accurate - for the individual who is posting them. Then we get the gun, and it really doesn't work out for us due to our personal style of shooting, differences in body styles and sizes, etc. So it may be an absolutely great gun for many - but just not for us. So we see it sitting idly in the gun carousel, not getting out to play very often, and make the decision to 're-home' it.
3) Being an accumulator as described above, I don't have room for too many air guns if I want to store them in an appropriate environment, protected, and in manner which keeps them in top functional and cosmetic condition. I have 2 gun carousels in my study where I can keep my airguns, and each one is in a silicone treated rifle sock to prevent getting dinged up. When I run out of room in my carousels, I don't currently have other good storage options, so time to sell something (for that next new gun which is, or which might soon be inbound).
I understand that I have worked hard and have been very fortunate in life and have the means to purchase, try and keep or sell multiple airguns. And that this does not apply to many. I count my blessings every day that I wake up on the correct side of the turf. And if I'm lucky I get to go out and shoot my airguns. And if I have a gun which doesn't work for me, or just doesn't get out to play often, I hope that I can make someone else's day when I put one up for sale at a deal price.