Look at wall street, people consider a 5% positive ROI in a year as doing *very well*. Imagine that buying a card new depreciates its resale value instantly by 30%, if you pay off the card in 4 months, that's a 70% ROI in 4 months. Admittedly it's riskier, but isn't that the name of the game? Don't like risk, go invest in blue chips (not that they're doing great these days).
There are a couple of differences here. Investing in the shares of a company is not like investing in bitcoin: the company does something and creates value. Bitcoin is just a commodity. Graphics cards are essentially worthless after 2 years. Increasing DirectX versions make previous card version obselete. A card may pay off itself in 4 months, but don't forget the case, PSU, CPU, ram, storage, and motherboard required to make that card work. Payoff time is now much longer.