Ok. So the reason that theists feel that the godless live empty lives is most likely because the theists tend to believe in an afterlife and "something more" and a purpose.
So it is imagined by theists, when they try to think about it, that being an atheist means when you die you are gone, and life is just a game of making money pointlessly to survive for a little while and die, everything you do and think and make ultimately amounting to nothing you can even eventually reap benefits from or enjoy.
Its like imagining a farmer working and toiling at planting and growing as they burn in the sun and decay and drop dead, the whole endeavour appearing to be futile and worthless as no sustained or much repeatable pleasure was earned or gained, just 60 to 80 years of worthless struggles and various sufferings and small pleasures with nothing in the end but wasted time.
The theists on the other hand imagine that they are struggling for a reason, that they often believe they will have eternal life or be given a great extension and that their actions and conduct have immediate as well as future and afterlife consequences and purpose which gives them more "meaning" as they relate to a goal that goes beyond the expected 60 to 80 years.
I love thinking about both ideas.
What if and what are the implications if your good deeds and bad deeds mostly amount to nothing, no one is watching and no one cares, you're on your own and your pain and pleasure is of no interest to anyone but yourself? You are born, forced and pressured to waste your limited time making money to survive, and in yiyr death everything is wiped for you as you can't even reminisce about anything or remember because you're dead and gone forever.
What implications are there if what you do does count for something that you can't escape later after you die?
