It’s Valve, their whole MO is finding what would be fun next. They don’t expend money on something for any reason other than, is it fun, is it fun to work on. If either answer is no, then it won’t even see the outside world. There’s rumors they have worked on several games up to relatively advanced levels of development (at least a playable gameplay loop) then dropped them altogether because something didn’t work out, and they never talk about it with anyone unless it is finally decided it will be a launched product. That’s why this closed testing is such a big deal, they’re letting people play it, which means they already played it internally for thousands of hours.
Another interesting pattern is that they don’t make games to tell stories. This has always been a misconception since Half-life has such massive following over the story, and hurt over unfinished plots. But if you check closely, those games where never about the story. Usually Valve makes something with a fun mechanic to play, then they work on writing a creative and cool story/dialogue around that gameplay. Never the other way around. 99% of their games are about gameplay, if you stripped all flavor text, voice dialogue and art from Portal it would still be a solid and extremely fun puzzle game.