Because, IMO, it combines the worst aspects of Java, Delphi and FP family traits in the same package.
Trying to follow what a Scala program does under the hood makes my head hurt. Following the edge cases through a forest of syntactical candy-floss is just too much. The plain Java parts are not bad, but the moment you pull out and nest all the special lispy shortcuts... from that point onwards I need to expend a big fraction of my brain cycles trying to figure out just what the hell the piece of code is actually doing. Or trying to do - because I can't properly trace the subtler logical parts.
And the end result is that, with Scala I do not feel qualified to assess your problem solving approach. Code should be written for computers to run, but for humans to understand.
if you ever care, the wizard book[1] can get you started with a toy implementation of prolog. it's just searching through a big state space, really not much to it. The key idea is unification. PAIP builds up to it in a nice way, and the scheme language spec has (had?) a nice unifier as an example[2].
it's also pretty reasonable to just say to hell with prolog, and go do other fun things with your life. But if you do care at some point, it's not magical. it's just a fancy search.
