The bar is raised and raid content needs to rival what Naxx gave us in Vanilla. People wouldn't be happy if MC/BWL/AQ were released these days because even though some bosses had interesting little quirks not all were very interesting fights.
I played so much WoW it aches to admit it and I have my idea: the answer to this is not simple, first it's a game design decision (issue?) from the ground up: to play EQ, very simple, you played with a handful of hotkeys and a chat box.
Now every WoW-clone and of course the original, makes you keybind something between 30 and 40 hotkeys (post culling). They are not all high priority buttons, thankfully or you'd have EQ2, but they are still there.
On top of this, they strayed away from "rotations" and used priority lists, so your list of things to do has a more varied pattern.
Then you have to look at their latest encounter design and the 4 different levels of difficulty to see how fucked up raid encounters are these days: just count the warnings from GTFO or DBM.
I thought that raids were cool because they felt epic (as an EQ noob being vaporized by lady Vox), then I appreciated a few gimmicks thrown in to keep people paying attention instead of watching TV (Molten Core), from there on it went (imo) downhill from a certain point of view: you no longer could afford dead weights in a raid, you needed very good healers working endlessly around stopcasting or the 5s rule, because you needed a fuckton more dps to pass some checks (Vael) or a coordinated group with able kiters (Razorgore). Up to and including LK, all fights required little more than positional awareness and it was good, because you could afford to fuckup and still recover (healers could make up for a lot of small mistakes and some big ones).
Nowadays if you do a fight like Emperor Mar'gok, you understand how crazy can a fight can become and of course the only way to have below average players doing it, is if every mistake they make is ignorable (LFR). In BRF there are already a couple bosses were the raid wipes in LFR difficulty and I suspect they could nerf it down even more.
Personally I'm done with WoD, got two months of fun and one of not so much fun. I don't like modern raiding, for me LK had the correct balance of good and bad and allowed people like me to play with less performing players without getting frustrated and advancing at a decent rate. We completed all normal mode raid tiers in LK with a super casual guild of 10 raiders, 2 or 3 of them being *quite* below average, playing one night per week, but we had fun and shit died relatively quickly.
In WoD I joined a similar guild (1/week) and in normal mode we couldn't kill shit because of underperformers.
Highmaul: Ko'ragh died twice, probably by mistake (or boredom). Mar'gok never died, not even once, I don't think we ever reached the last phase with orbs.
BRF: we hit hard enrage 3 times on Beastlord (I was as a brewmaster 2nd on the parse), before killing him one week later, we were 3/10 (Gruul, Darmak, Hans Franz) and couldn't kill Oregorger for both dps and mechanics. So yeah, some players were not good enough.
I could scout for a different place, but the guys are nice and I didn't want to leave them screwed, so once a window of opportunity opened (alliance with another guild that covered my tank slot) I decided to quit, because I had little to no fun. I prefer easy raids and carrying friends to dance dance revolution competitions and wipefests.
I'd say to Blizzard: first no enrage timers in normal mode, second, pick a random encounter mechanic and remove it and third... make that shit 1-groupable. Some people just don't like to raid. Leave heroic for real raiders and mythic for crazies.
6.1 was a fucking joke: let's consider BRF part of the patch, so raiders were happy. Everyone else got... a selfie camera and twitter implementation. What the fuck? Unless you consider playing facebook games in your garrison part of an MMO. As Mr Creed said: they are just pissing money away because they can.