why computers stink at chess

  I've found for the most part that computers aren't so great at chess.  They are so predictable?  Is it the programmer, or is it that the chess programs just can't compete with humans.  I've played some version of fritz my old friend use to have, and even that wasn't much of a challenge.  Oh well, I'll have to see if the new version isn't 10,000 dollars USD, if it is, I'm not buying it, because I'll only pay $5 USD in a yard sale for it.