That's exactly my point -- there is no such speculation. But there ought to be such speculation, at least preliminarily, if one is arguing that SOMEONE planted bombs in the building because the "burning jet fuel alone" explanation is scientifically implausible.As for China or Russia playing a part. Find me just one page or any article or any speculation whatsoever that either is involved.
Let me repeat this for you: all your arguments-from-metallurgy can (in principle) show scientifically that there were explosives placed in the buildings ahead of time. But metallurgy and other scientific arguments do not justify leaping to the conclusion that the explosives were placed by the US government -- nor do they justify ruling out the possibility that China or Russia or Belgium planted the explosives.
So, the reason that there are thousands of conspiracy pages arguing that the US planned 9/11, but zero conspiracy pages arguing that China or Russia or Belgium did it, has nothing to do with "basic scientific facts" that a high-school student could understand, and everything to do with the political biases that conspiracy-theorists bring to the table.