I agree, but this isn’t one of those things. It’s not hard to obtain in the slightest and the only reason why one might call it “exclusive” is because Blizz decided to arbitrarily take it away. It’s literally just install Classic, create a Death Knight, and play for a couple hours. Not even remotely difficult.
There is absolutely no reason to remove it beyond creating an artificial sense of fomo. I would, in fact, argue that it is more detrimental to remove it, for Classic in particular, than to keep it. It’s supposed to attract people in to try out Classic and perhaps convince them to keep playing Classic, thus promoting the population of Classic servers and keeping Classic players subbed.
However, this is a bad time for that as it is in direct competition with Dragonflight. Either the fomo will drag people away from Dragonflight launch, the fomo will be ineffective and people won’t go past the required DK starting zone thus not accomplishing what Blizz set out to do, or Dragonflight will draw people away from Classic. This is NOT the time to try to compete with their own product
If they allow the promotion to remain evergreen, however, then later on when people inevitably get bored of Dragonflight, rather than unsubbing they might figure why not make a Classic DK, give it a try, worst case scenario I get a mount out of it. And since they are bored of Dragonflight, the promotional hook might actually work and convince that person to keep playing Classic and keep their sub going.
What they are doing with this mount is shortsighted and straight up stupid. But that’s been Blizzards MO for a long tome now, cash in on the short term, screw long term profits.
So yeah, having exclusive and difficult to get things is perfectly fine. But this ain’t one of them. Go look at Qiraji black mount, Gladiator mounts, the Mage Tower book, etc, for actual good examples of exclusive and difficult to get things.