I recently looked at MMO Champions achievement raiding data and the complaints from recruitment, It doesn't look good. I think the problem is Progression and the way this is handled. Lets take a look at a fresh level 100. A fresh 100 (even alts) has to go through getting 610 gear (lol dungeons almost dead), has to go through HM LFR (ilv615), then has to go through BRF LFR or normal HM, then has to go through each difficulty of each raid tier (N,HM,) and finally has through go through RNGesus himself in order to get a tier set, and then only then will you be allowed to apply to a good guild to do Mythic...Do you see the problem with multiple difficulty settings and no safety net.
The problem isn't that raids are hard (heck, i like the challenge), the problem is getting there. One way to solve this would be to decrease the high item level disparity (Someone who is 685 full tier set will out dps someone without it by 40k dps or more) but that wouldn't feel like good progression.
What I suggest doing is increase tier set loot and bring back justice/valor points to make progression faster and to get more guilds to do mythic (when everyone has BRF heroic gear, there's only one more place to go).