That's not really true at all. The original design was that legendary items were rare and you'd have maybe one or two of them in your guild. They were also usually class specific. You HAD to raid to get them. Blizzard made it so that everybody got a generic legendary item in MoP and WoD and let you do it in LFR and then even made it more casual than that by letting them drop from World Quests. You can literally get a legendary item without raiding. This is 100% the result of the casual audience trying to make it easier and easier to get legendary items.