Because I am not thinking about 20 years later.
I am thinking about how much I like it now but I have only had it for a few months. How well do they hold their value after 20 years?
I am sure you do like yours now, but in 20 years (or maybe 10 or even 5) there will be a newer, smaller, lighter, quieter, etc.. can on the market that you will want. Nothing says you cannot keep your old one, but I was never using my old one, so I sold it. Value was close to what I paid for it, but who knows what it will be in the future.