Because you'd think some dipshit would value a secret and surprise for players globally more than getting some stupid Internet spoiler-karma-attention.
I know that's not the case with anybody. Everyone values attention whoring much more than the collective feel goods of everyone else. I mean, what is the fucking value of spoiling the surprise aside attention whoring or just being a dick. Everyone could have had an exciting Un-event full of surprises as Wizards intended but some retard wanted to "be first" and dropped the surprise.
So yes, some fucker spoiled it. If Wizards had not released the visual spoiler some fucker would have spoiled it too, except with an entire spoiler you could simply avoid it. Personally I don't care about being spoiled but I'm pretty sure all the people out there attending events would have rather not known that there was secret shit that existed outside the official spoiler.