Not vouching for creatine, but in general, humans get some vital nutrients from animal consumption. Vegans have to take some B-vitamins for best health due to what they don't get from meat. I assume creatine is the same.
Today, because our food / water are so sterilized (good thing!), we don't typically get much bacterial B12 from unclean root vegetables, drinking from streams, etc. So yes, we need to supplement today. Because of advances in cleanliness.