All the info that comes out before the show is very controlled. If it comes out beforehand, they want you to know it because its frivolous information that won't even matter by the end of the season.
If you're mad that you read the mattress spoiler, then why did they include it in the portrait trailer? Obviously the producers want you to watch THAT. It's going to happen within the first 2 or 3 episodes and then it will be dropped/become irrelevant. That's why they'd rather throw it out and get hype out of it instead.
I've been following this show for spoilers since Murder House ended and its never amounted to anything substantial. They haven't even finished writing the story ffs

They'll be brainstorming and throwing out scripts all the way through January to come up with the final episodes, just like with Coven.