Why is it that this always happens, the EC, the Nerevarine, and in TES 5 the coc will be probably done, why do they keep having these warriors, who defeated unspeakable evils and defeated gods suddenly disappear?
Because there would be a dragon break otherwise. You might have played as a male character, someone else might have played as a female. Different gender, different class, different race, different factions.... Beth can't make them appear again because if they suddenly said "oh, the Nerevarine was a guy, he joined the Morag Tong, and is an Argonian Nightblade..." Well, gee, thanks, but that's not
my Nerevarine.