The tooling is ultra specialized and requires whole teams of highly skilled techs to assemble and calibrate. That's like half the cost involved, and the crews running the lines don't know much about how it works, they don't need to. If something goes wrong, they have service contracts.
So China can glean some of the process, but, because the design, assembly, and setup of the machines is done by western contractors, they're effectively locked out of 'the hard part'. Not to say they can't learn it, it's just not nearly as trivial as the rest of the things they clone.
Also worth noting that, many of the chinese clones are made in the same plants as the orignals, sometimes in parallel to the originals as to benefit from existing successful processes that were already in place, but using cheaper materials, less QC, different branding, etc.
It's actually quite impressive engineering really, they can often reduce part count and cost significantly while shipping a functional, albeit inferior, product. Chip fabs don't work in that model though, so, that presents an additional difficulty.