I think that it has to do with the fact that the one major obstacle to the development of socialism around the world is US unipolarity. Effectively, the US and its satellite states have been acting as a sort of vanguard of capital worldwide, helping national bourgeoisies to strangle their own left-wing movements, which in turn brings them the confidence of these national bourgeoisies, helping to maintain US unipolarity. Thus, to help socialism spread, China must break US unipolarity. And to break US unipolarity, China will effectively need to win over the confidence of national bourgeoisies all over the world, in the process breaking the international bourgeoisie’s class consciousness. Now, “exporting” revolution is unlikely to achieve this, as it will only antagonise the national bourgeoisies of their countries, forcing them into the US’s arms. What instead China needs to do is to economically invest into the 3rd world so that the national bourgeoisies of these countries, which are also the victims of western imperialism, albeit to a lesser extent than the proletariat, come to see China as a friend and the US as an enemy. In that way, these newly pro-China national bourgeoisies are more vulnerable to home-grown socialist movements, and the US’s role as a Vanguard of Capital is reduced as, due to having less resources to imperialise over, its own ability to crush left-wing movements in its sphere is reduced. What China can also do is support homegrown socialist movements that do manage to take power on their own so that they don’t then fall to reaction (for example, Venezuela). This would also have the advantage of meaning that, was socialism in China to fall, these would be less dependent on China then, say, the Eastern Block was on the USSR, making their socialism more likely to persist.

To summarise, what China needs to do, and is doing, to spread socialism is to break the unity of the bourgeoisie on an international scale by providing an alternative to capitalist-imperialism for the national bourgeoisies of the 3rd world, leaving them to be isolated from the bourgeoisies of the Imperial Core when it comes to resisting socialism, and also weakening the Imperial Core as the supply of foreign resources and labour for its capital to exploit is reduced. Then, it can help socialist movements strong enough to come to power on their own survive. This would, in my opinion, be better than exporting the revolution.

PS: Sorry for the wall of text, and for replying a bit late; I thought about this.