why might rulers of command and socailist economies see market-oriented reforms as a threat to their leadership

because these market-oriented reforms impose greater freedom economy and consequently increases the power of private property. Recognizing that socialists system are based in the control of the individual, in an ideological, social, cultural and economic way. Especially in the property rights sphere, this ideology advocates for the collectivization of means of production. As a result, the socialist state and its leader's would lose total control over its population.

The reason why the leaders of the countries with command and socialist economies would see the market economies as a threat to their leadership is because they will lose the power they have over the production, the land, the resources, the laborers.

In a market economy, pretty much everything is privately owned, and the government can only be regulating things in accordance to the law, but can not control the profit and the work of the companies. In a command or socialist economy, the leader of the country has total control over everything, thus controlling the whole profit of the country and how everything will be done, so by allowing a market economy, the leader will be directly affected with losing a lot of power from his hands.