Although they also intermarried with the natives (many fur traders married Indian women), I would argue that the key reason was that they learned the art of reciprocity with the natives. The French went to the Americas primarily to trade - as well as to conduct military operations and establish missions - and they chose to establish a relationship of mutual respect with the Native peoples, taking, nevertheless, advantage of the alliances and the rivalries that already existed among the different tribes. They traded the furs of animals that the Native Americans obtained and prepared for them, in exchange for European goods such as firearms, cloth, sewing needles, cooking utensils made out of metals, horses, and alcohol. The gain, therefore, was mutual, and, despite their cultural differences, I believe they learned how to reciprocate and benefit from each other.
They learned the art of reciprocity with the natives
Explanation
The French practiced the exchanging of things with others for mutual benefits. Unlike with the English, they were less interested in land. French practiced assimilation system of colonization were individuals were taught ways of life of the French people including language and culture and later accepted as one of their own. In addition, the French were Catholics and their missionaries did not insist that the natives should forsake their own was of worshiping to adopt Christianity.
