Bearing in mind that the Korbanos of all the Nesi'im were identical, why does the Torah repeat the Korban of each Nasi? Why did it not present the details by the Korban of Nachshon ben Aminadav, and continue "ve'Chein Hikriv ... " by each subsequent Nasi on his day?
Ramban #1 (on Pasuk 2): Hakadosh-Baruch-Hu confers honor upon those who fear Him. Consequently, bearing in mind that all the Nesi'im thought to bring their Korban and to inaugurate the Mizbe'ach simultaneously, and that it was impossible for each Nasi to be the first to bring, Hashem honored all of them by repeating all the details by each one.
Ramban #2 (on Pasuk 2, citing Midrashim): Because each Nasi had a different reason in mind
Ramban: In fact, Nachshon ben Aminadav had in mind all the reasons cited by Rashi
Why does the Torah insert the words "Hikriv es Korbano" by Nesanel ben Tzu'ar, which it did not do by any of the other Nesi'im?
Rashi: Because the tribe of Reuven claimed that, if Yehudah preceded them, they ought to come next, since Reuven was the firstborn. So Moshe informed them that he was merely following Divine instructions
Rashi: In fact, the word "Hikriv", in Pasuk19, which is written minus a 'Vav', can be read 'Hakrev!' a Lashon of command, to hint that Nesanel ben Tzu'ar was to follow Nachshoon ben Aminadav.