‘And Yahweh spoke to Moses, saying,'
Once again it is stressed that this command came from Yahweh through Moses. But when we consider Leviticus 11:1 and Leviticus 13:1 we must ask, why only to Moses? The answer is probably because in this case the priests are not called on to judge anything. No one is required in order to declare that there has been a birth, the midwives would declare on the sex of the baby, and all would know the position with regard to cleanness and uncleanness. The expertise of the priests was not required.
Again we have to note that the only limit on this section timewise is the death of Moses. But whenever it was given the mention of circumcision, which was not practised in the wilderness, was seen as preparation for a future in the land of Canaan (as specifically with houses later (Leviticus 14:34)). As the people waited in Kadesh almost on the border of the land, they still lived in expectancy of finally entering the land, and the Law was designed to encourage them in their expectation.