Here's a really interesting thread from the MMO-Champion forums: Why Do You Choose LFR Over Raid Guilds? There's a lot of chatter about LFR, and how negative the experience is, etc. So one person decided to ask about the other side of the coin, and the responses are extremely enlightening.
The main reason given, naturally, is time and scheduling concerns. This was predictable, and indeed is a strength of LFR.
However, the other major trend is that a lot of people hated the raid guild atmosphere. The drama, the way people were treated, etc.
If LFR is widely considered to be a negative experience in terms of the people involved, it should be of major concern that many people see the raid guilds as worse. That LFR actually provides them with a more pleasurable experience, in addition to being more convenient.
I really like proper, extended raiding with a solid raid team. I am lucky enough to be in one in The Old Republic. But if a majority, or even a significant minority, find LFR to be a better experience than raid guilds, then there's no way raid guilds will survive.