Standing in damage is bad because your health is dropping. That's the feedback. If someone is ignoring all of the feedback showing bad stuff happening to you in game, I don't know what you're expecting Blizzard to do, short of a giant GTFO flashing across your screen and locking out all of your action bars until you move.
Do you like extensive tutorials before single-player games teaching you how to move the camera around and look up and down too?
I'm not saying LFR is perfect, or that Blizzard can't improve the game mode, because there's always room for improvement. But somehow shifting the responsibility to Blizzard to basically play the game for everyone in LFR and/or teach them how to play is a little far-fetched. Why is it so ridiculous to expect players to actually do something themselves? This is why Proving Grounds Silver continues to be a source of QQ on WoW General.
Problem with alot of lfr players, isn't that they're bad, it's because they're intentionally being bad while either afk/tunneling while watching a tv show on the side etc/drunk/tired of doing lfr for the 1000th time etc/or waiting for an opportune time to grief.
Part of this is the aforementioned issues with legendaries being locked to raiding, and I due to think it's related to alts, maybe they should have made the legendaries server wide for characters on that account.
As for Blizzard, the money of a casual player is the same as the money of a hardcore raider. They need to keep their hooks into them, and that's where they need to adjust (even though I doubt many casuals are doing LFR). I'm just providing my feedback as a player who lost his patience after nonstop wipes on Nazgrim/Dark Shamans in lfr back in Pandaria, and is no longer playing, not that my word is gospel or anything, and everybody has the same experience as me, but I do think they have to reevaluate their strategy on LFR/Legendaries/etc.