thats actually its pretty simple to answer
most people are not born as leaders only born as natural followers.
thats why they will never form the group even if they are experienced but will gladly join someone elses group
thats why LoL/Dota are such popular because people can use "1 click - join group " mechanic.
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dont judge because different people have different goals in game - there is hundreds of thousands of ex-raiders who in past raided high difficulties but cba anymore - and lfr is perfeckt because you can ignore idiots in pugs only automatickly join and do easy mode.
the burnout of high difficulties of raiding is real - it requires special kind of people to raid more then 1 expansion or even 1-2 tiers on schedule in a row . and pugging is pure toxicity so lfr>pugs any time of day and night.