Because they don't care... I literally pugged the EP glory because my guild didn't do it, done by achievement hunting community that didn't even have any strict requirements, it's done on normal mode so you don't even need a lot of gear just don't take the piss.
I'd say most people don't have it because they cba dedicating 2-3 hours to get 1 mount. Which is still much less effort than doing all m+ on 15, getting pvp mount or getting mythic raid mount (if not bought carry), all of these take much longer than 3 hours.