Killmonger was beyond saving so he needed to be put down. And he needs to stay put down for at least the next movie. Resurrecting Erik this earlier would both mess up that last brilliant moment in the film, mess up both T'Challa and Erik's arcs, and it will be a sign that Coogler and co have no confidence in Chadwick's T'Challa to carry his franchise and that Coogler for some reason can't work without MBJ playing a major part in his film. I can imagine the latter part as well as doing a sequel would be new and have it's own pressure for Coogler and his team, but really I think he's done a good job writing and directing T'Challa, and he can continue to do that.