Could it be that previous titles did not sell? Or that some ingame content was tricky for that country. Or that distributors didn't want to sell it? Or or...?
This earlier post says:
Well at the time GK was released, Sierra changed distributor in Spain from Erbe to Coktel Educative, which only translated about 3 or 4 games since...
Regarding this, I think it's mainly a distributor issue... Perhaps as you said; because the previous titles didn't sell that well or something...
Also, I don't know how you exactly discovered what got translated and what didn't, but apart from the lack of information (on the 'net) on it, there's also a lot of (IMHO) faulty information (hello Adventureland!)...
Like the fact I'm still not convinced that Police Quest (SCI11) Spanish exists, since I've seen no real evidence... As far as I know, Police Quest was the last AGI2SCI remake Sierra made (SCI11, instead of SCI1 with other remakes, IIRC) and wasn't translated... Furthermore I *believe* the SCI remakes weren't translated to French and German... Which makes sense, since they didn't bring the cash Sierra expected...