Singularity: There is really good reasons to withhold information about possible releases?
JMich: Yes.
The following is all speculation on my part.
Scenario 1) Negotiations fall through, for whatever reason.
A few years back GOG had said that they had signed one of the big 5 (Take 2, LucasArt, Microsoft, Square Enix, EA) and that they were close to signing a second one. Those were EA and Square Enix, though they were obviously in talks with the others as well. My guess is (and has been for a year or more) that the LA talks were also going well, but then LA was purchased by Disney. All those talks became null and void overnight. If GOG had told us back in 2012 that the were closed to signing LucasArt, then took over 2 years to bring them here, there would have been riots (most likely contained in the forum, but riots nonetheless).
Scenario 2) They can't get a game working.
The most prominent cases here are Carmageddon, which was promised as a Kickstarter reward, and it (barely) made its deadline, but it was released in a buggy state, and Chaos Overlords, which is the game that caused me to
terrify a blue. The game still has a ton of issues, as can be seen by the supported OSes on its
gamepage. So promising they'll release a game, then postpone it due to technical reasons is also a pain.
Scenario 3) They are still evaluating a game.
This is mostly for newer games, and Dark Matter was a prime example. The game was released here on Day 1, and removed from sale on Day 7 if I recall correctly. Since then, GOG tries a bit harder to properly veto the games t hey release, since that was a fiscal fiasco for them.
So, tl;dr version. They don't like to announce in advance what games they have plans to release, in case they cannot keep said promise.
In addition to that, they may not legally be at liberty to discuss negotiations for new publishers or new games because those details may be covered under NDA.
