Human breast milk oligosaccharides

Human milk oligosaccharides can not be digested by humans or bacteria - why are they there? 

22:31 Bifidobacterium sticks to the walls, prevents any other bacteria from coming there, so that basically nothing bad gets to the walls, so you can actually see the disappearance over time if you look back over time at poop samples

http://www.wnycstudios.org/story/the-elixir-of-life/