Why especially those?
replyYour body can synthesize creatine, so it's not essential, but meat is a source of exogenous creatine and eating it results in higher stored creatine levels, which is slightly good for muscle power endurance in the ~5-15 second effort range. Supplementing produces slightly higher relative improvements in creatine levels in vegetarians and vegans than it does in people who eat meat.
replyBecause they lack all kinds of substances that meateaters get plenty of.
replyI'm a vegan, and I'm surprised this is downvoted, because it's true. There are plenty of things that you need to be careful to not become deficient in on a vegan diet: protein (in appropriate amino acid balances), creatine, b12, the good Omega 3s (from algae preferably; flax is missing DHA entirely), calcium, iron, to name a few.
replyYou're fine if you take daily algae oil, multivitamin, iron supplement, calcium, and creatine (without going overboard on any of it) and making sure to get lots of protein from balanced sources (eating a ton of soy is actually not a bad idea, because it's a balanced protein), but I wouldn't recommend somebody who doesn't want to have to worry about their nutrition to go vegan. Enough omnivores are already deficient in vitamins and minerals, and veganism only makes it harder.
Nobody gets fired for supplementing vegans.
replyBecause meat is the best source of creatine from diet.
replyWell, if vegetarians and those of the Vegan religion don't get enough creatine it is most likely related to them not partaking of an important source of the substance: meat.
replyNot 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.
replyWhere do those animals get their B12 from, do you think? (Hint: they don't synthesize it either, they get it from their diet)
replyToday, 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.