Why is it not surprising that several battles took place near the Bozeman Trail?

Because the Bozeman went through Sioux sacred grounds of the Black Hills and they had been promised by the US government that they would retain the land of the Black Hills. The government by setting up forts and allowing wagons through broke the treaty they had with the Sioux nation. When the Union army finally gave up Ft. Laramie the fort was promptly burned to the ground by the Sioux.