For gods to desire sacrifice and worship there must be a benefit of some nature conveyed by such acts and if there was such a benefit then surely they would appear in before humans and display their powers to gain the worship of those humans, but they don't.
Why is this? They must be limited by something but if they are limited by something what is it and how can they hold power and be limited at the same time?
It must be that a God is absorbing the faith of the other gods and then not performing actions, thereby they rob the other gods of the ability to perform actions and thereby gain followers but at the same time they don't appear themselves and convert people anymore which again makes us wonder what the reason for that is?
Perhaps it was not a God at all that has absorbed the worlds faith but an Anti-God, the aim of this Anti-God was to rob the gods of the ability to perform any actions that would gather faith and power to them and once that was done they would not perform actions themselves and so they would see faith and the power brought from faith die.
It's also possible this Anti-God was absorbing the faith of other gods but they themself had nothing to give back, they could only consume.