Bison is a very lean meat.
It is fat that makes a burger juicy and tasty.
So if you make a burger using Bison meat, you need to add some kind of fat .. and some breadcrumbs to help absorb whatever fat there is.
It would be a waste of money to take a prime cut of steak such as ribeye and grind it up for a burger. The best cuts for burgers come from the shoulder cuts, and have about 15% fat (in beef, at least).
With Bison, you would want to cook the burgers in beef tallow or bacon grease just to give some fat and flavor to the meat.
From a culinary/flavor standpoint.
If you are cutting back on animal fats for diet and health, then you would just cook up the bison meat without adding fat. But it would not be a burger-to-die-for (literally and figuratively speaking, of course).