It's because Sejta has a mad amount of crit (he's gemming/reforging into crit to gain more rage) when critting with wrath from HotW it does upwards of 300k dmg per hit.
Just to clarify for non-druids:
Sejta does gem alot of crit, but its also great for his own survival (More rage).
Yes HOTW is to be nerfed, and yes its very good. I pulled 90k DPS on dummy with spellcaster weapon switch as feral + pot (No buffes or two-hand staff, so could be even better + I have no speciel gear). HOTW is great for that boss sure.
One reason for WoW decline I often hear is that its an old game and naturally people get bored with it. But TV is much older and people still watch that. Surely if a thing you once enjoyed keept staying fun, you would still use it?