Farmers' enthusiasm for production is only a consideration. After the society developed to a certain extent, the slave owners became real vested interest groups. They can easily obtain most of the country's social wealth according to the enfeoffment system. This distribution is not good for the bottom working people and the country. If the central government's revenue is small, the central government will be weak and the war preparation expenditure will be insufficient. You will encounter great problems during the Warring States Period. Therefore, it is necessary to reform the economic interest base of slave owners seeking profits. If the land is not allowed to buy and sell freely, then the land will always be in the hands of slave owners at all levels. That won't solve anything. Therefore, others must be allowed to acquire land in a market-oriented way. Land sales are allowed. Therefore, Shang Yang offended many vested interests and came to a miserable end. But he cleared the institutional obstacles for the development of feudal system. People who get a lot of land gradually become emerging landlords.

The reason for land annexation is indeed private ownership of land. This score is much better than that for slaves. Later, it did cause many social problems, even the dynasties changed constantly, and the peasant uprising continued, which was the weakness of the feudal system. Every system has problems, but it applies to different levels of productivity. But we can't go backwards just because there are such and such problems.