I've read an article recently about the M 2013 core set and it states that:
Well, everyone knows creature enchantments aren’t playable...
Why exactly creature enchantments aren't playable? I'm talking about the context of Constructed games.
The simple, no-frills answer: creature enchantments aren't generally playable because they offer your opponent an easy 2-for-1 (or better, if you're the sort of person who likes to load creatures up with multiple Auras...)
Any removal spell that would have previously just taken out your creature now takes out all enchantments on that creature too, giving your opponent an easy route to significant card advantage. Not a situation you want to enter into lightly.
EDIT: The OP asked in the comments about Totem Armor. See this article by Mark Rosewater, in which he says:
Straight from the horse's mouth there!
The line you quote was, in that review, actually parodying the 'groupthink' that says that enchantments are never playable because of the risk of two-for-ones that thesunneversets's answer describes. While this is a good perspective to have in general, every card has to be evaluated on its own merits, and it's not uncommon for specific enchantments to offer so much power (or, notably, for the hexproof creatures available to be good enough) that they override this rule. Rancor itself is an exception because it mitigates the card-disadvantage problem by going back to hand for the next creature, making it more like an equipment than an enchantment in many ways; Moldervine Cloak served a similar role in a few decks from the original Ravnica-era standard; and just a year ago Angelic Destiny was a regular player in Blue-White aggro decks, as the perfect way of suiting up a Geist of St. Traft.