1)
Why does it repeat "Ka'asher Kasuv b'Soras Moshe"?
1.
Rashi: This hints that Hashem testified that if we transgress the Shevu'ah, He will bring against us all this evil.
2.
Malbim: Since the latter curses came, this shows that the previous curses already came to make them repent, but they did not help.
2)
Why does it say "v'Lo Chilinu Es Pnei Hashem"?
1.
Malbim: These curses were not for punishment, rather, to make them repent, and we did not heed them. We attributed them to chance. Therefore, Hashem brought the curses in Devarim for punishment.
