1)
Why does it say "Aleichem"?
1.
Rashi citing Targum Yonasan: Due to your sins.
2.
Radak: In the nations' lands, rain and dew descended. In your land, they were withheld, and even dew, which is not held back. And so it says "u'Nasati Es Shemeichem ka'Barzel" (Vayikra 26:19).
3.
Malbim: Until now, the curse was not with special Hashgachah from Hashem. Rather, Shamayim and the Ma'arachah held back dew. The land held back its produce based on nature. From now and onwards, the punishment will be via Hashgachah.
