The problem with castling is that for a move that is only once done in a chess game we have to keep track of a couple of variables and do a check for every move

The problem with castling is that for a move that is only once done in a chess game we have to keep track of a couple of variables and do a check for every move in the tree. It is rather unpleasant to code and it will increase the program size and decrease the speed (by a bit I mean). May be that is because they ended up not implementing castling.