Once upon a time, sets were spoiled months in advance on a regular bases. People in play testing would AIM Daron Rutter, known as ‘Rancored Elf,’ all of the new card information and he would give that information to the internet. But, this led to Wizards having to deal with things they didn’t want to deal with. It all came to a head when people started writing Wizards angry letters about how Frazzle should have stayed 2U, like it was in play testing. (Information they never really should’ve had to complain about.) These leaks changed public perception of upcoming sets and affected sales. So, Wizards sued Rancored Elf.[1]

Thus, now leaks like this one are rare, and normally people get fired over them. Like what happened with the New Phyrexia “God Book” a few years ago, these spoilers will affect public opinion of the set.[2] They will affect sales.

And, before you say you’ll not let these spoilers bias you, I recommend you read this wiki page.