The focus here is on the people’s dissatisfaction with the manna that God had miraculously provided. They remembered the very interesting diet when they were in Egypt of fish and vegetables of leeks, onions and garlic. “Why couldn’t God give us something more pleasant?” Whether they had enough livestock for meat is less important in the narrative than their carping complaints. They had cattle, sheep and goats and they would have eaten some of them, although of course if they ate too many of them then they would no longer have them. God could have replied: “You already have some animals for meat. Why not be satisfied with your occasional meat meal, and be grateful for the miraculously provided manna?” Perhaps if God had chosen to give a detailed literal response that would have been it. I have googled for alternative answers but unfortunately none of the answers I found made much sense. The answer seems to be in the state of mind of the people, not in the state of their herd.