Okay nobody was able to tell me why they take probiotics but upon doing some research here are some concerns:
From Breaking the Vicious Cycle by Elaine gottschall. Many probiotic/yoghurt companies are putting Inlulin/FOS (fructo-oligossaccharides) into there product. They are thought to feed "healthy bacteria". But they also feed Klebsiella. She even mentions this is implicated in AS. She did say Natren is against doing so. Inlulin is also known as Neosugar, alant starch, alantin, dahlin, helenin and diabetic sugar.
FOS is found naturally in artichokes. But she implied I beleive that it is safe in it's natural form.