LFR was fine for how it was introduced because it was based on the fact that the better players will use it to farm what they wanted faster (Tier sets/Legendary Quests) and it worked the way Blizzard intended it to.
Many people started "raiding", then they saw that people that arent braindead were joining, they would die/afk and the boss would still die with 10 people, and this became acceptible and a trend 2 tiers after.
Even the newest player can read "I am doing 20% of the damage the others are doing and i die, and i get free items, why bother playing lol".
Then the better players complained about putting rewards that they had to do (like weekly Valor cap, or generally caps that had you going in LFR), and they removed those, then they removed tiers, and the incentive for any better player to even bother disappeared.
And then LFR became unplayable for almost 3 years until 9.2 cause people went back to being "forced" to do LFR for tier sets, and the quality returned slightly, but also the slacking.
As example on my main, we killed Jailer (not a tier set boss, but there was a tank bag
at 23:30 and i was bored) from 50% to 0 with like 8 people? 1 tank 1 healer 6 proper DPS, so he melted, but thats not the intended way.
Everything they add to the game, has a reason, but the community finds a way to completely destroy it for themselves.