If you read some of the comments and news posts on Steam the whole thing is a bit of a mess. Many games are still being held back and removed by Steam, usually with no communication from Steam about it. Oddly the slide puzzles are doing fine though.
Take
You must be registered to see the links
as a example, have a look at
You must be registered to see the links
then
You must be registered to see the links
and finally
You must be registered to see the links
. Looks like it will finally be
You must be registered to see the links
, but it took a lot of time and effort dealing with them.
I'm still waiting for
You must be registered to see the links
... Scenes
You must be registered to see the links
are probably holding it back, but it's the core of the game and the company releasing are seemingly just leaving it in release limbo.
For games like
You must be registered to see the links
, I would think the way they're works in progress wouldn't go to well on Steam (although GP seems to be doing ok). There are usually very few people making the game too (sometimes with other full time jobs), I doubt they have the times to deal with Steam and make the game as well.