Because they wish it was because Kerry would win right now. Kerry will be found out and Bush will unleash everything on this guy that will make Kerry look like the biggest liberal in the world.
The analyst know this is not over and they want the Republican base to put up the white flag. Kerry will lose and he will lose "BIG TIME."
That's it exactly!
The key to this election is the Republican turnout. If conservatives, especially evanangelical Christians, turn out to vote, Kerry cannot win. Period. Hence, the attempt to depress Republican turnout by calling it all over in August.