The Steam top sellers list is ordered by revenue, not units sold, so each Index they sell is worth 20-30x of a game sale in the rankings.
Hence why Counter Strike 2 is the #2 "top seller" despite ostensibly being free - it's counting revenue.
> And it used to be much more expensive back when it was at the top.
The price actually hasn't moved at all, the full Index kit still costs the same $999 it launched at in 2019. The cheaper SKU on the charts is just the headset without the controllers or base stations, which they only started offering relatively recently, but you still need to have controllers and base stations to use it. The headset alone being as high as it is implies that most of the people still buying Index hardware are existing Index/Vive owners who want to renew or upgrade their existing Lighthouse setup, and few are investing in a complete brand new Index setup today.
[1] https://store.steampowered.com/search/?l=english&filter=tops...