Yes MoP was probably the best expansion so far, the world worked excellent, flying worked excellent. Everything was good. WoD however is on the dead opposite side of the spectrum, please never put these two expansions together. When it came to exploration of the world, rare spawns and treasures in MoP was revolutionary, they tried something new for the first time. adding lots of random interesting and challenging content scattered all over the world and flying mounts was a very nice way to explore and find things.
Then near end of MoP things started to go horribly wrong. Firstly they started making rare spawns pop up on your map as skulls because they weren't easy enough to find for noobs.
Moving on to WoD, rare spawns still skulls on the map but turned into worthless boring normal mobs that could be killed just once as a "rare?" and gave you all the interesting loot it could possibly drop right away, such service... -_- However, since there was no flying you could often see these skulls on the mini map. the game letting you know there is a rare spawn in that direction but no way of finding out if its even reachable or hidden behind a quest objective to open an entrance or only accessible at lvl100 through a teleportation of a quest or whatever.
The treasures turned into epic glowing things: ---> LOOK HERE, ITS A HIDDEN ITEM, GOOD JOB FINDING IT <------ that you could click and feel very satisfied after doing such an amazing job of finding it. But ofc should you miss one you could always get a map of all of them in the zone from a vendor or for free after clearing all quests in the zone. /facepalm
So yeah, I can understand how some feel no need of flying out and explore the world like you could in Pandaria and there it was awesome, now turned into some kind of kinder-garden.