It's just the author's choice of words - a question of style. Maybe he feels that there is a greater degree of difference between "terrible" and "bad."
All three words would mean more or less the same thing when describing chess, but In the context of chess strategy, the word "bad" would typically be use in articles intended for advanced players only.
The word "horrible" might tend to used in an article intended for amateurs, or beginners, or those who know little about the game.