They just cannot make realistic computer opponents that don't give up pieces at the first sign of trouble. I was playing in Chessmaster against one of their opponents nominally rated at like 1950, which is certainly stronger than I am. I had a winning position in a bishop endgame, I was about to penetrate on the kingside, but he had some counterplay and it wasn't sewn up at all. But it would be tricky. The computer's response was to trade his bishop for a pawn. It seems that whenever the computer gets into a tricky position and it's trying to play weakly, it just gives up a piece. This is not realistic, no human player, especially not one rated 1950, would make that particular mistake.
Slightly more annoying is the recap they give at the end and the annotations: since the computer never resigns, one must play through to mate. They have a "worst move" and "missed mates" feature, and their utility is hampered by the fact that I don't care to play the absolute most accurate way when I'm a rook up, so if I lose a pawn or take 10 moves to mate instead of 5, those show up, but I really only care about the part of the game before I got my decisive advantage or where my opponent got the decisive advantage, not where the evaluation changed from +80.31 to +50.32 (FYI, +1.00 is usually winning).