Looking at a chip makes it easier, but it is still millions (or billions in the case of a CPU) of dollars for engineers to figure it all out. That doesn't get you to understand what was done or why so 2-3 years latter you can make that chip but they have now moved on to a faster/better version and you are behind. And of course if you try this Apple (or whoever you copy) will have plenty of engineers who can look at your chip and in just a few hours decide there is enough to have lawyers sue you for the copy.

China already has plenty of engineers who can make a chip, and experience with making CPUs. ARM licenses a lot of useful things for making a CPU (I don't know what). They would be better off in the long run making the chips they all ready understand better. Which is something they are doing. It takes longer and costs more, but because they understand they can also customize the next chip for something they think is good - if they are right they can be ahead of everyone else.

What China is lacking is the fabs to make a CPU. They have made good progress in building them, but there is a lot of technology that isn't in the chip that is needed to make a chip.

It took cerebras less than a billion to get to where they are now, CPUs are not that hard. You would probably be able to reverse engineer them for ~100 million