Thanks for the chapter!
Gotta love politics. MC didn't really explain all the details but no matter how powerful the Bei Li Empire is it can't take on everybody at once. So if it had declared war and taken Utor other nations might worry about being next. However, by having Ke Xi trick Gang Yi city into taking it they can make up an excuse like Utor had asked them for help, or couldn't stand seeing Gang Yi ruthlessly attack their beloved neighbor or several other reasons that would be enough to keep other nations from seeing them as the bad guy or banding together against them. Hence they get all of Ke Xi's research for free, an excuse to take Utor and Gang Yi city, and appear as good guys rather than a greedy hoard bent on world domination. As for Ke Xi she could claim was just following orders from her lord who was determined to expand her territory and had strongly argued against invading Utor, or if caught could be disavowed as faking being part of Bei Li Empire or had been fired a long time ago due to issues and whose location was being sought after and acting on her own.