I wouldn't have thought that either but, you live and learn.
The survey is about time played, though, which could be very different from sales. I'll check out new games but often won't spend too long on them if it's a short indie adventure, or it turns out I don't really enjoy it whereas, with an old game I'm familiar with like Civ IV, I'll happily spend 10 hours on a single campaign.
Also, multiplayer games that people sink a lot of time into can take a while to get established. I know Fortnite's not on Steam, but that was a 2017 game, and is still massively popular all this time later. Steam has games like Team Fortress which probably still have large communities.
It's a surprising figure but shouldn't be setting off any alarm bells IMO.