Flying is a form of travel, of which there are many others, not an "integral feature" of wow. You people need to get over yourselves, it's getting quite embarrassing tbh.
Leaving a game because they changed a travel mechanic is laughable at best.
"Hey Johnny, not seen you on wow for a while? You've been playing since [insert xpac here] and uses to be on all the time, what happened? Get bored of raiding? Pvp not your thing any more? Just get bored of the game?"
"they removed flying mounts. It was an integral feature in the game you know? I just couldn't bring myself to have to travel around in a different, slightly slower manner, so I quit forever."
Honestly, don't you see how ridiculous you all sound?.