How is it a non-sequitur? It doesn’t make sense to build infrastructure to support population growth in an area where you are deliberately reducing the population.
They're not expecting to reduce the population. The claims of "genocide" are based on a rather stretched redefinition to include forced cultural assimilation. And the US has more than its fair share of both forced cultural assimilation and deliberate efforts to reduce certain populations, so even if we accept your arguments then that's still no reason to have worse transportation.
The birthrates in Xinjiang are plummeting as a consequence of forced sterilization. Your genocide denial aside, the demographics of the region don’t favor your argument.