experience farm

good day
I wanted to know why the server has disabled experience from some mobs. In the Howling Fjord location, you could raise experience from level 68 to 75 on seals, it was always like that on all servers. this is one of the places where tanks could get experience by farming a spot and develop a little faster. also mages who play through mass damage also farmed there. I arrived in Northrend after getting level 68, I hoped to finish my hero to level 80 at least by farming spots, and not by dull tasks. why don't they give experience? why can you play in five windows, but you can't farm your daughter in packs?