The main reason is that they did not try to change the Natives. They also did not compete with the Natives for land. When the French first came to the Americas in the 1530s and 1540s to engage in seasonal fur trading, they immediately established strong trading ties with the local Natives they found there. The Natives already dealt extensively in furs.
The French quickly discovered they could go back to France in the winter months with ships laden with furs they had purchased from the Natives with European wares, such as metal cooking pots, weapons, horses, and other goods not accessible to the Natives at that time. The Natives also accompanied the French on hunting parties and showed them where the good fur animals could be found. The French made it a point to learn the Native languages and ways, and established good relations that were based on equality with all of the tribes in the area.
The French began to stay year-round in the early 1600s, establishing their first permanent settlement at Quebec in 1608, one year after the English founded Jamestown in Virginia. They did not displace any Natives in the establishment of their settlement and continued to work closely with them in the fur trade. They respected Native territories, their ways, and treated them as the human beings they were. The Natives, in turn, treated the French as trusted friends. More intermarriages took place between French settlers and Native Americans than with any other European group.
This close alliance, which was based on mutual respect and good treatment from both sides, led the Natives to side with the French in their conflicts with the English settlers that came later in the 1600s and into the mid-1700s. Relations between the Natives and the English were not nearly as good.
The English treated the Natives as inferior, believed they stood in the way of their God-given right to the land in America and tried to subject the Natives to their laws as they established their colonies. The Spanish didn’t have any better relations with the Natives, as they tried to enslave them when they first came to America, and later established missions where they tried to force them to convert from their traditional religions to Catholicism. The Natives did not appreciate any of this.
The key to the friendly relations the French enjoyed with the Natives was all in the way they treated them when they first encountered them, and how they continued to treat them afterward. As long as the French maintained settlements in America, they enjoyed excellent relations with each other. For those who have early American French ancestry, or French settler ancestors who married Native Americans, the vast majority of those records can be found in the provincial archives of Quebec (some records there might lead back to France if the settler returned there with his Native American bride).
These records provide a fascinating look at relations between Natives and Europeans and show just how different things could have been if all the European people who came to America had been as progressive in their treatment of the Natives as the French were.