Nah, the new type speculation and rumours appear every generation. But this time, there wasn't really anything contradicting them, actually quite the opposite. GameFreak have repeatedly addressed the typings of Sylveon, Xerneas and Yveltal, but they haven't given as much as a hint until last Sunday. They could have ignored the type question entirely - as they did with the species names, for instance, but they kept posting those ???s wherever they could. They want us to discuss the typings.
As for why "Fairy" is the most popular theory... well, I guessed it's partly because of the obviousness of (as well as vehement opposition to) a Light type (which half the fans want to complement Dark, and the other half want just to make the former shut up about it). Fairy became the most prominent theory because of Sylveon's appearance. It's too damn hard to label as anything else. "Fairy" is also a label that could be put on very many existing Pokémon across all generations, thus making a retype less "forced". This is unlike other proposed types, such as "Love", "Sound", "Glass", "Gem", etc. Also, a fairy type would cater to the crowd of Pokémon-playing girls, offering them some Pokémon that retain their cuteness upon evolution, but also gets butt-kicking powers (see Aron and Whismur versus Skitty and Jigglypuff). Fairy simply seems plausible, and GameFreak has done nothing to dampen the rumours.
Come the next generation, though, and I guess a Light type crowd will return. Until we get it, those rumours will never die down. If we do get it, though, I guess they would just find something else to wish for.