They're working on a fantasy title too (https://lightnofire.com/) which uses the same engine to build a whole planet, but Earth scale.
Improvements in the engine for one, translate to the other.
It also now marks it as a "great value" so people are more likely to pick it up even if they don't end up playing.
Depending on pricing, you can even just sell to people upgrading or changing consoles (this is one area that really helps Stardew Valley, albeit with a low cost).
After all, even if you've sold millions of copies, there's way more people who have NOT bought it.
https://en.wikipedia.org/wiki/No_Man%27s_Sky#Sales
> After the game was added to the Xbox Game Pass service in June 2020, Hello Games reported a month later that No Man's Sky had seen more than one million new players.
It’s surprising to see its continued popularity and development. In a good way of course!