“Russia doesn’t have the capital, manpower, or equipment to complete this project.” (Power of Siberia 2 Natural Gas pipeline)
There is a stretch of the planned route that is over 1,000 miles long, over tundra (which melts into swamp during the Summers) where no roads yet exist. Berms would have to be built first, upon which to lay a road, and build the pipeline. Might need a railroad, for the volume of material required.
Nobody else on Earth is crazy enough to bite off that much construction to nowhere, when other projects can make better returns on capital, at lower risk.
It is China or no one for Russia. They will have take whatever terms China dictates. Even if they do, China still might not really want to take the risk with this project.
Such a project would be much like building the Alaskan highway over the same terrain - there must be videos on YT showing just how difficult it would be.