New hardware justifies new software, etc. Eventually, they'd like to sell you another game. You're more likely to buy that game if you've "kept up."
Anecdotally, most PC gamers I know unintentionally go in 2-3 year cycles for upgrades - usually the GPU. It's not planned, it's just when things start feeling underperforming. Often after upgrades, people binge old games they already owned but now at higher settings or FPS.