This week, I discovered another reason why that is: Timing expansions.
Over the last decade or so, expansions have become a more and more common an expected aspect of gaming, but each one comes with questions unrelated to game balance.
Claustrophobia
Keep in mind: I don't have inside information on sales here. All I have is what CROC and others have said on BoardGameGeek and elsewhere.
If you release an expansion too soon, you run the risk of publishing an expansion for an unpopular game. You also run the risk of repulsing late buyers - "Am I going to have to buy expansions to play this, too?" Or of alienating completists who see it as just a money grab.
On the other hand, if you wait too long you run the risk of people moving on to other games. Three Dragon Ante
The best counter-example to this is, Nuclear War has been around since 1965. Nuclear Escalation hit nearly twenty years later, and did well enough that Nuclear Proliferation hit a decade after that ...
Dungeon Twister
You also need to keep in mind the designer's timing - Christophe Boelinger put out Dungeon Twister: Prison
While I'm briefly on the subject of DT, there is a poll on BoardGameGeek that I'd like you to take (if you haven't already).
It's a tricky juggling act, publishing games. It's a bit like running a store - you need to be passionate about gaming. You need to love games and gamers. But you can't lose sight of the fact that it's a business. You need to make money.
And that, my friends, is where I would fail.