Why was TAMSK removed from the GIPF series?
Because of the time element (making it not a pure abstract strategy game like the others in the project).

Production costs were higher for that game than others in the series, due mostly to the timers. The designer has noted that that is what keeps it from being reprinted at the moment (in 2008). But it's just speculation to say that that is a reason for its removal. 

The designer says that it was removed because it didn't fit with the rest of the series: the rest were all pure abstract.

From this blog post:


  But I also want to stress once more that it was not removed because it was not good enough. I like TAMSK a lot—and also SMART is convinced of its qualities—but I cannot deny that it appeals to another public than most players who like pure abstract strategy games.
  Feb 5, 2008