I agree with you.
They don't have that many serials made and are at war. And we've all seen evidence that the Su-57 is active in this war. It would be actually quite stupid if they brought a serial one to this airshow. And if PLA are not interested in buying one, why bother.
End of the day, if PLA gets some, it will be purely political considerations to help the Russians. The new geopolitical alliance between Russia and China means this could very well happen.
Also having Su-57 perform aggressor roles is not a bad idea especially if India acquires some.