Attention span is at an all time low, I'll admit, but I also wonder how much of it is just because something doesn't align with their personal wants and opinions. I had an old work acquaintance who, though I can't remember what show it was- GoT, maybe? Walking Dead? - would miss incredibly obvious things, even things that were spelled out, just because it didn't align with where they wanted certain characters to go or things to happen. The willful ignorance is just as bad as the inadvertent. I feel like it happens a lot with character deaths and romances- there's always the "well, we didn't see a body" or the "so-and-so could still get together even if one of them killed/assaulted/expressed their disinterest, etc." No matter how much the writing tells you something just isn't going to happen, people will still choose to believe otherwise.
Maybe it's a side effect of writers giving in to fan demands one too many times? Or fans feeling like they've guessed a beat/twist, regardless of how easily spottable it was. There is a weird sense of entitlement when it comes to some people and their favorite shows.