While they had lived in Egypt, the Israelites were controlled by slave masters who oppressed them for forced labour (Ex 1:11-13). When Moses led them into the Promised Land, they left the authority of their slave masters behind. All that remained were their family connections. As they marched through the wilderness, they naturally linked up as families, clans and tribes, because these were the people they knew and trusted.
God had already established this family-based social structure among his people. In the promised land, Moses discovered that, the “tens fifties, hundreds and thousands” are the glue that holds society together (Deut 1:15).
He had more dealings with the leaders of thousands, so he listed them first, but the actual structure worked the other way round, as tens, fifties, hundreds and thousands.
We have not noticed, but this was a radical change. In Egypt, everything was controlled from the top down. A slave master had control over a bunch of Israelites, because Pharaoh had delegated authority to him. He could make the Israelites do whatever he liked. The Israelites could not get married or have children without getting permission. They could not choose where they wanted to live. The rest of Egyptian society was structured under the same top-down authority.
The land in Egypt was owned by Pharaoh (Gen 47:20-21). He controlled who got which piece of land to grow food, and had the right to take most of what they produced in return. In the Promised Land, the land was allocated to tribes and families by ballot (Num 26:52-56). Every family would have a piece of land and the leaders of tribes could take it off them or controlled how they used. In fact, they were given a moral obligation to ensure that each family retained its inheritance in the land (Lev 25:8-54).