The transitory period of New Economic Policy lasted only a few years in USSR

Who’s to say that’s the best length of time for a transitory period, in all countries? Why are you sure you’re right and China’s leadership is wrong? If the USSR could allow limited private control of businesses for a time and then revoke that, why can’t China?

Note that Mao himself was far from strictly opposed to private ownership of capital, at least as long as the national bourgeoisie did not seek to undermine the socialist project:

In our country, the contradiction between the working class and the national bourgeoisie comes under the category of contradictions among the people. By and large, the class struggle between the two is a class struggle within the ranks of the people, because the Chinese national bourgeoisie has a dual character. In the period of the bourgeois-democratic revolution, it had both a revolutionary and a conciliationist side to its character. In the period of the socialist revolution, exploitation of the working class for profit constitutes one side of the character of the national bourgeoisie, while its support of the Constitution and its willingness to accept socialist transformation constitute the other. The national bourgeoisie differs from the imperialists, the landlords and the bureaucrat-capitalists. The contradiction between the national bourgeoisie and the working class is one between exploiter and exploited, and is by nature antagonistic. But in the concrete conditions of China, this antagonistic contradiction between the two classes, if properly handled, can be transformed into a non-antagonistic one and be resolved by peaceful methods. However, the contradiction between the working class and the national bourgeoisie will change into a contradiction between ourselves and the enemy if we do not handle it properly and do not follow the policy of uniting with, criticizing and educating the national bourgeoisie, or if the national bourgeoisie does not accept this policy of ours.