According to the Wikipedia article on the An-225 (https://en.wikipedia.org/wiki/Antonov_An-225_Mriya), Antonov has produced exactly one complete and in-service An-225. A second, incomplete airframe exists in Ukraine.
So these aircraft are essentially handmade.
The single complete An-225 is being leased commericially to fly super heavy cargos worldwide. The charter isn’t cheap given the aircraft’s size and fuel consumption. In addition, the maximum takeoff and landing weights for this aircraft limit the airfields this aircraft can be operated from.
It all comes down to the number of missions requiring this unique aircraft’s capabilities. So far, worldwide demand hasn’t even been enough to justify completing the second airframe.
Just how many new build An-225s (or the Chinese variant) can the projected Chinese mission requirement justify building? Two? Three?
The point is technology. If they know how to build this they can build more suitable aircraft too.
But the main thing is the engines they already got. Before that they were literally stone age in that department. That among 9ther things meant their bomber force had very limited range and performance. Now things are changing.