Many people have extra dedicated desktops for video games, audio, sewing, local firewalls, DLNA, etc. These are hobbies that require it. That's not going to change anytime soon, if ever. Also, for many folks, these days, their daily system isn't even a desktop, but a tablet or laptop.
For casual users, not long-term hobby, it's a transient need. Build computer from parts, use, parts then available for next task. I'm often amazed at just how many people "still have" older computers/parts in closets/attic/basement/etc. Because if I wasn't doing video, which has the obvious legacy hardware needs, I'd never keep old stuff lying around. I'd be sold or recycled.
BTW, just this morning, while watching a game show, the prize was a year subscription to a record club (vinyls). Huh? They have such things? What's next? That prize was about as interesting as a phone booth or butter churn.