I think many of us who started playing MMOs in our teens ~10 years ago, are now at a stage in life whereby we can't dedicate the time that we used to. There are games out there that cater to the hardcore market and its no coincidence that they have no player base.
People with a massive amount of time to dedicate to MMOs are in the majority these days and majority rules; especially when they are the ones with the money.
This whole hardcore/casual debate has little to do with making quests epic. After a year or two even the casual players in EQ had their epics. They may not have been first, but they were never excluded. EQ doesn't care if you complete your epic in two days or over three years. It will give you your reward just the same.
The truth is rather more simple...
1. Many people today want to play alone. They consider working with others to be "hassle" and resent having to spend time with social aspects of MMOs, such as networking and helping others.
2. People want rewards more often. People would rather kill 10 mobs and get a bit of XP and a minor item, than quest for two weeks for one reward. As much as us old-timers hate "kill 10 frogs" quests, others love them for their simplicity and as a way of being distracted from the grind.
3. The "we don't read" or "ADHD and proud" brigade. How many times have you watched a player click through text because reading is boring? How many times have you listened to player ask how to complete a quests because they skipped reading the quest text? In WoW this was the norm it seemed. Forget reading the instructions, grab the quests and ask in general chat for someone to tell you what to do.
4. Spoiler sites. When EQ epic quests were put in, spoiler sites were just beginning to pop up. Now every detail of every quest in any MMO is online within days. How do you make a quest feel epic when your playerbase are all following walkthroughs?
Sadly, I agree that the days of MMOs being graphical MUDs are long-gone, and unlikely to ever return.