I don't think LFG/LFR really killed the community. I'd blame shrinking/mismanaged server populations causing a feed back loop of the community getting worse so people quit so the community gets worse. LFG/LFR is a good tool, but it needs to facilitate guild recruitment and friending other players. I've met some great people in LFG, and the sad thing was I couldn't get to their server or play with them again because it costs money. Right now battle groups and cross realm zones are a confusing cluster. Assuming the structure hasn't changed from how I think it is. Not playing for years puts you out of touch with how things work.

All that and content droughts. It's real easy to come back, gear up, and clear everything, and quit again. No real reason to stick around, especially if your server sucks. I think that's a big part of the appeal of vanilla/ progress servers. You have people running content instead of having everyone at max level running 1 raid that means anything.