How does the altar of rebirth would I have over 500,000 dead troops and yet can never revive them?

dont completly understand the question but for the altar of rebirth:

only severaly wounded troops that no longer fit into your hospital get sent there. Troops that are dead immedietly during the fight cannot be revived.

If you have troops in the altar of rebirth you need special resource from the altar to revive your troops, that resource is gained over time with different factors affecting its gaining speed, which are explained in the altar.