curses and blessings

Parshat Ki Savo

In Chapter 27 Moshe is setting the nation up to receive a set of blessings and curses. The representatives of the tribes are setting up on the mountains of Gerizim and Eval and when the Levites called out a blessing towards those on Mt. Gerizim and they respond amen and then the corrsponding curse towards Mt. Eval and those standing there would call out amen.

The interesting thing I noticed is that the Torah, when listing the blessings and curses, only lists the curses. If it was going to choose one or the other, why did it choose the curses and not the blessings? Another reason for the assumption is that the blessings were mentioned first and the curses second, so the first item (blessings) is what should have been listed in the Torah, if only one was going to be listed? Furthermore, a few verses later the Torah lists a number of generic blessings for listening to the word of Hashem and then it lists the corresponding curses for not listening - if it listed both the blessings and the curses there, why not here as well?

I have not thought of a satisfactory answer yet at this point. Maybe one of my readers can suggest an answer... if you do please post it in the comments.

When searching through the commentaries, I noticed that the Seforno deals with the issue of why only the curses were mentioned.He suggests the reason to say it in the form of the curse was to separate the curses so only the people deserving of the curse will receive it, rather than all of Israel. I did not completely understand hsi reasoning and why it is true, and am still looking for an answer..