“Accept these from them, that they may be used in the service of the tent of meeting, and give them to the Levites, to each man according to his service.”
Numbers 7:5

The offerings of the tribal chiefs were immediately after the fiery deaths of Nadab and Abihu who were killed for offering unauthorized incense. Everyone must have been very careful in how they approached God and made offerings that day, and God had to explicitly order Moses to accept the gifts.