I don’t think mankind has given up on a God so much as they have diminished Him. They have taken Him off His throne as absolute righteous Judge and omnipotent creator and turns Him into a kindly if not doddering old man who winks at their sin and just wants to be sure everyone has a good time. That is a greater sin than forgetting Him. God will not be mocked
Even as redeemed and dearly beloved children and heirs I think Christians forget just how powerful righteous just and holy our Father is.
Like those wily potentates like Putin and Merkel, neither hot nor cold, good friends in divinity, making hay out of their heritage.