As you are so knowledgeable in these things, what's a point to remove a game from steam? Even if it sell very little, with right discount it still sells over time (not talking about Acti here, that's other matter entirely)
And I know that Konami doesn't make sense most of the time, it's just general question.
99% of the time it's due to legal reasons, such as a publishing contract expiring or a licence lapsing. The other 1% of the time it's due to something dumb, like EA yanking Crysis 2 and Dragon Age 2 to prop up Origin or Atari yanking Ghostbusters and Riddick because magical fairies told it to.