What do we learn from "ha'Zevachim u'Minchah... ba'Midbar Arba'im Shanah"?
Rashi citing Chagigah 6b: Is my desire Zevachim and Menachos? In the Midbar, I did not tell (command) your Avos to offer Zevachim to Me. I said "Adam Ki Yakriv" (Vayikra 1:2) - when he wants to offer. "Va'Ya'asu Bnei Yisrael Es ha'Pasach b'Mo'ado" (Bamidbar 9:2) - this teaches that they offered only one Pesach in the Midbar. Radak - this is disgraceful for Bnei Yisrael.
Radak: The prefix Hei introduces a question. Did you offer to Me Zevachim and Minchah in the Midbar for 40 years, like it says in Yirmeyah, "Ki Lo Dibarti Es Avoseichem v'Lo Tzivisim b'Yom Hotzi'i Osam me'Eretz Egypt Al Divrei Olah va'Zevach"; I explained there (refer to Yirmeyah 7:22:1:2-4). Chazal said (Chagigah 6b) "ha'Asuyah b'Har Sinai" (Bamidbar 28:6) - some say that its actions were said at Sinai, but it was not offered [in the Midbar]. Others say that it was offered there, and did not cease. Shevet Levi, who did not serve idolatry, offered it. "Mi la'Shem Elai va'Ye'asfu Elav Kol Bnei Levi" (Shemos 32:26). Yisrael, who served idolatry, did not offer.
Malbim: They were in the Midbar for 40 years. They did not have many animals for Korbanos 1 and wine for Nesachim. Their primary Avodah was doing Mishpat and Tzedakah - "Tzidkas Hashem Asah u'Mishpatav Im Yisrael" (Devarim 33:21).
"U'Mikneh Rav Hayah li'Vnei Reuven ve'li'Vnei Gad Atzum Me'od" (Bamidbar 32:1)! Perhaps the other Shevatim had few. Or, for some reason, few were Kosher for Korbanos. Or, perhaps this was only after taking the spoils of Sichon and Og; during the 40 years, they had few. (PF)