This is the cause why Joshua did circumcise: all the people who came forth out of Egypt, who were males, even all the men of war, died in the wilderness by the way, after they came forth out of Egypt.
With the completion of the circumcision, the people could celebrate the Passover (something that an uncircumcised person was not allowed to do; see Exodus 12:47-49). The journey from Egypt to Canaan was now officially over, and therefore the miraculous daily supply of manna ceased (10-12; cf. Exodus 16:35).