Why are Napoleon's foreign policies linked with his personal interests when France gained form them?
It is not clear that France actually did gain from Napoleon's ambitions. At the end of these wars, was France truly better off than it would have been if Napoleon had not tried to gain an empire? That is not clear.
However, if we assume that France did gain, it still makes sense to link Napoleon's foreign policies to his personal interests. This is because (one can argue) it was only because of Napoleon's desire for power that these foreign policies were undertaken. If Napoleon had not come to power, it is possible that whoever did come to power would not have been so hungry to conquer. By this argument, Napoleon's foreign policy did not come about because of France's needs but rather because of Napoleon's need for power. In this view, France may have gained, but the real goal of the foreign policy was to fulfill Napoleon's desires.
So the issue here is really about what the driving force was behind the foreign policy. If the whole goal was to fulfill Napoleon's ambitions, then the foreign policy was about him, regardless of what impacts it had on France. The intent of the policies would have been connected to Napoleon's personal ambitions, not to the good of France.