Same reason as Cao cao, While Sun is a great man (in his time), but he didn't unite China, which effectively means he has never led china. He is a great scholar, intellectual and revolutionary, but as a politician he is less effective and certainly is not a ruler. As such, I don't deem him fit as a leader choice.
If Qing, Mao, Wu, Tang taizong, Ming taizhu belong to the first tier of chinese leaders, Sun belongs to the second tier, at best.
China needs Liu Bang. Gave the race its name.