Farmers do water vegetables with water that is not safe to drink, they spray diluted sewage onto vegetables as a cheap fertilizer, runoff from adjacent livestock operations flows into cropland, etc. The difference is that meat is generally cooked before consumption, which kills a lot of bacteria, while many vegetables are eaten raw. You are probably in more danger of getting food poisoning from alfalfa sprouts than you are from a t-bone.
(Ok, that was a bit of a cheat. Sprouts of all varieties and leafy greens are usually the worst when it comes to veggie contamination while undercooked chicken and ground beef are the worst for meats. I am picking my examples at two extreme ends of each group to make a point, but hopefully the real point you will get from this is that there are a lot of factors that go into food poisoning risk assessment...)