Combination of Catch up gear getting players into this tier LFR before they have exp playing the toon to any level, Flex keeping more better players out for less carry, and most predominately, the culture that is LFR where its the things to do.. to just auto attack the boss while tabbed out.
No reason for the decent players to go into LFR when they have Flex available now, so LFR is left with poor quality players.
I don't really understand why people who have done Flex, Normal, Heroic SoO go into LFR and then complain the standard of players in there is shit.
During ToThc progress we recruited a hunter that was in a random guild on our server and had only ever raided in LFR, no previous experience in other expansions etc. She's now our back-up DPS and happy to raid whenever we need her, her IRL is quite busy so she didn't want to commit to fixed times, which suits everyone well. I have to say, she's actually one of the best players I've ever raided with, in terms of knowing her class, understanding mechanics etc. She eases into heroic progression raids, and pulls really high numbers considering her gear is ~9-10 ilvls below the rest of the raid.
What I'm trying to say is that LFR in 5.2/5.3 had a few gems there. Flex most likely pulled them out, or those gems decided they wanted to try normal progress.
LFR is awful, people who say they "Don't need gear but go there for Valor Points" are crazy. By the time you've cleared LFR for your 90 valor or whatever it is, you could have completed 10 Heroic Scenarios to be valor capped in an hour xD
Only time I've ever been into LFR this tier was the 2nd part when a casual guildie wanted me to help him through some tacs there. We had 4 people staying at the top of the tower fighting and shouting at each other to let them into the cannon because they were the best at it.. /slits wrists