Why did the Israelites need manna when they had so many sheep for sacrifice?

Answer 1

Sacrifice was extremely important to the Israelites, so may have been given high priority. It is also very likely that the animals had been consumed by then. I think the manna was nutritionally superior, being a complete food and sustained them for many years.

Answer 2

One of the great puzzles of the story of the Exodus is that the Israelites believed they would die of hunger because they had no food (Exodus 16:3), yet they had rich herds of sheep and cattle. This can best be explained by the scholarly view that the Book of Exodus was not written until many centuries after the time attributed to the Exodus. When writing of the hardships of the Israelites, the author simply did not check back to the point in the story where it was explained that the Israelites took their livestock with them.

Answer 3

Rashi commentary addresses this question explicitly (on Numbers 11:4), removing the apparent puzzle. They had no lack of livestock, but they wanted food provided by God. The Torah criticizes them in keeping with the high standard that was expected of them, but their request was actually motivated by a desire to see God manifest his power.