Because DF-27 would be an overkill if you put them in anywhere in China except for Northeast.
There is only ocean and more ocean in the middle of nowhere in Pacific within the extended range once DF-26 upgrading to DF-27. Or they could be put in Xinjiang to deter against countries in the Europe but what is the purpose of it since Europe is not particularly a concern for China except for their shallow rhetoric.
Primary target for DF-27 (personally) should be a conventional attack against Sheymal and Clear Early Warning radar stations as well as hedge against GBI or NGI at Fort Greely. It only needs 6,500 km to reach these target and HGV is a great asset to counter against EWS. So theoretically!!! it could be used as a maximalist demonstration attack without crossing nuclear threshold to begin a full out nuclear war.
But I find hard to understand the necessity of DF-27. For me, it is either "do it or not" option on attacking your adversaries' mainland, no need to destroy EWS to demonstrate your capability. Or it could be simply PLARF wants to have a tool to hold movable asset at risk anywhere in the world by employing HGV on IRBM or even ICBM.
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